2 x 4 Quick Fuel Carb Tuning

[The Real McCoy]

I have a 428 stroked to 462 with a 63 low riser intake that runs rich based off plug and exhaust coloration, very black.  The engine runs and drives reasonably well other than the black exhaust.  It was put in the car in mid June and probably has 1500 miles on it now. When the break in oil was changed at about 500 miles the oil was quite black for the low miles on a brand new engine.  That is what really got me thinking about it being rich as it actually runs and drives fine but was concerned about the soot in the oil.  I recently added a wide band oxygen sensor which verified it is running rich, at idle it was reading 10.9 to 11.4.  Going down the road at cruise speed it pretty much stayed between 11 to 11.5 from 2000 to 2800 RPM.  Coasting only got it up to 11.6.  The Idle Mixture screws do not seem to be able to lean it out when idling.  I even turned them all the way in and it only come up to 11.7 t0 12.0.  Road testing with them screwed all the way in netted about the same during the cruise test 11.7 to 12.0.  Coasting now come up to 13 -14+.  Idle was actually a bit rougher than when the mixture screws were turned out a 1/2 turn, that is where they had been set prior to getting the oxygen sensor installed.

This is the setup.
428 bored .030 with 4.25 stroke kit from Survival.
9.8:1 Mahle Pistons
406 Heads with CJ size valves.
63 427 Cast Iron Headers
Comp 280H Cam
63 427 Low Riser 2 x 4 Intake
t-10 4 speed
63 Galaxie
Runs on 91 octane non oxy gas.
The oxygen sensor bung is welded in to the exhaust pipe about 3" behind the header outlet on the curb side of the car.  (427 cast iron headers)

The carbs are Quick Fuel 750 vacuum secondaries
Primary jets 72
Secondary jets 82
Primary idle air bleed 73
Secondary idle air bleed 33
Primary idle feed restriction 33
Secondary idle feed restriction 40

All float levels are between 1/8 to 3/8 up the sight glass.  Fuel pressure is right at 6.5 pounds.  It does idle reasonably well at 900-1000 RPM and vacuum at idle is 13-15".  I pulled the carbs and checked the throttle plates, the idle transfer slots were barely visible on the primary side and were not at all visible on the secondary side.  If I were to open the secondary enough to expose the idle transfer slot I think it would be running way over 1000 RPM, seems they have to be open quite a bit to expose the slots....

I had ordered some 68 and 70 jets for the primary side when I ordered the wide band oxygen sensor but have not put them in just yet after seeing how rich it is at an idle.  I'm thinking the problem is more to do with the idle circuit than the main jet size.  I did speak with Quick Fuel today and the person recommended changing the primary idle air bleed from 73 to 76 and the secondary idle air bleed from 33 to 45.  Seemed like quite a jump on the secondary but I did order some new idle air bleed jets tonight.

So a few questions....
Will the main jets do anything at all for the rich readings at idle? 
Does Quick Fuel recommendation on the idle air bleeds seem reasonable?
Other things that I may be missing....

[machoneman]

So a few questions....
Will the main jets do anything at all for the rich readings at idle? 
-nope, not at all.
Does Quick Fuel recommendation on the idle air bleeds seem reasonable?
-yes.
Other things that I may be missing....
-power valve equipped? You didn't say. PV numbers?
-weak spark at idle? Strong spark when yanking a plug wire or the coil wire?

[Barry_R]

Put the jets in.  The cruise and hard throttle values say the combination "wants" that.  Get the easy range clean and then start chasing the transient and idle factors.  Do not get too fixated on the O2 numbers at idle - tune for the behavior and keep an eye on the plugs.  The O2 numbers at low speeds might be useful for guidance - but they might not be.  I have been told by folks that know this stuff better than I that less expensive and older design O2 sensors lack resolution and accuracy at low gas speeds and require higher speeds and temperatures to provide good data.  On the dual quad stuff I often find them to idle best at 1/2-3/4 turn out once everything is sorted on the dyno.  Milder combinations with two fours do not require much idle air or fuel to gain RPM - idle air comes from throttle blade circumference and you have a lot of that....

[The Real McCoy]

Thanks for the replies

-power valve equipped? You didn't say. PV numbers?
 Power Valve is a 6.5 with a 52 channel restriction.
 
-weak spark at idle? Strong spark when yanking a plug wire or the coil wire?
 I hadn't really thought much about the spark as it runs and starts good but I will check that tonight.  For the record it is a new Pertronix III distributor with matching coil.  Initial timing is at 12 BTDC and goes to 36, I think it is all in by 3000 but would need to verify that.  Right now the vacuum advance is hooked to the manifold port.  I had originally hooked it to the ported fitting.

Barry's post....
I will put the Main jets in first and see what it does on the "cruise" test.  The one thing that worries me is the sensor stays low, in the mid 11's, when coasting. With the mixtures screws all the way in the readings did come up a lot during the coast part of the test, well over 14 at times, RPM would have been in the 2500 to 2800.  I guess that made me think it was the idle circuit causing the richness.  Running the screw in had an incremental effect on the idle and cruise test but a significant effect on the coast test.

The gauge and sensor are an AEM X Series with a Bosch LSU 4.9 Sensor.  Any opinions on this device?

I agree on the 1/2 to 3/4 out, it has always run good at those settings.

Also agree on the idle air comment, as mentioned the throttle plates are pretty well closed down and not into the transition slots, opening them at all will have it well over 1000 RPM.

What are your thoughts on Quick Fuels recommendations for idle air bleeds?  It seemed like a pretty big change to me to go from 33 to 45 on the secondary side.

[e philpott]

on the air bleeds , bigger is leaner ..... short of knowing the difference between the secondary low speed circuit and primary you just about have to start at QF recommendations and go from there

[Barry_R]

Closed throttle coast will pull plenty of vacuum and fuel through the idle circuits - I would worry about that last - if I worried at all.  The Quick Fuel guy is trying to get you some idle adjustability - directionally correct if necessary - if you can't get good idle behavior.  Tune the idle for behavior, let the numbers be what they are.  If you can't get it to idle and drive out of idle nicely and are way out of rational position on the screws - make the change and try again.

I have zero experience on that sensor kit and cannot comment.  But on some of my EFI stuff they idle best with numbers that are wonky and then straighten out once we get some RPM going.

[turbohunter]

On your last question, "what are your thoughts on the air bleeds".
I can say that my experience with a QF carb is the same as your two.
In talking with others it seems that they send them out very safe/fat.
I ended up opening my idle bleeds up to 78 from 70. I had bought a range of bleeds up to 84.
When to much bleed was installed you could definitely tell because of idle surging.
Ended up that 78 was the sweet spot. So that is quite a bit over the shipped size, just as they are recommending to you.

[The Real McCoy]

Thanks to all for the feedback.  I will get the main jets in see how it runs out and then consider changing the idle air bleeds if necessary.  I have the 68 and 70 main jets and should see the QF recommended idle air bleeds by tomorrow PM.  Work schedule may interfere with this project but will post results when I get it done.  Hopefully with some good results and less questions.

[Falcon67]

I think you are on the right track with the air bleeds.  I had the opposite issue with my 302 tunnel ram setup and a pair of Edelbrock 600s - the idle circuit was fine out of the box but the carbs needed 4% bump in fuel primary and secondary to get the best power mixture.  Opening up the idle air bleeds should give you some adjustment in the mix needles.  On a 4 corner they are still pretty sensitive when the air bleeds are right, the DP carbs I built with QF parts only like about 1/8 turn out to set idle mix.

[427LX]

This is all very interesting!
I run a 427 Windsor with good flowing TFS Highport heads 330/258 cfm @.600 lift with a .600 lift/242/249 hyd. roller.
My intake is a Price Motorsport dual Holley setup designed off of a Medium Riser FE intake.
Got it going with a pair of 600 Holley 1850's and the idle and off idle cruise was perfect with the stock .028 IFR and .070 IAB.
Would cruise nicely in the low 14's AFR.
Recently I swapped out the stock 1 9/16 600 baseplates for the QFT 750 plates with 1 11/16 throttle plates.
Right off this thing wanted more idle fuel the higher the cruise RPM went before transition to the mains.
It would stumble and go lean in the 15's at around 2000 RPM up with the curb idle being in the 13's.
Finally ended up with .033 IFR much like a 750 carb and .068 IAB's in the front carb which is primary and .070 in rear carb.
Now it's back to a nice 14.3 2000 RPM  cruise at light throttle in 4th or 5th gear.
Also went up 1 jet in primaries from 67 to 68 with same 68 in secondary jet blocks.

On your QFT carbs you might want to check ALL the air bleeds for any debris that might be clogging one up.
I find it strange that your engine was running with the Idle mix screws screwed all the way in! Fuel was coming from someplace and if an air bleed is plugged up it can siphon fuel out and into the venturi causing rich idle. I had that happen once!

[The Real McCoy]

I finally got some time to work on the carburetors this week.  Lots of things going on that kept me from doing much the last 2 weeks.

So I changed the primary main jets on both carburetors from 72 to 68.  This really didn't seem to do much for it, O2 value at idle was still down in the 11's.  The cruise test was also about the same as before the jet change.  At 3000 RPM it did lean it out a bit with O2 numbers in the 12.5:1 range.  I didn't mention in my original post that the car does have a 3.00:1 rear end so the cruise test is generally in the 2000 to 2600 range.  70 MPH is about 2700 and 3000 is pushing 80 MPH.  Just to see how the primary carburetor reacts to the RPM I run it up to 2500 and monitored the main fuel system with the air cleaner off, no fuel was coming out of the main fuel system.  At 3000 RPM I had fuel coming out of the main fuel system.  This was with the car sitting still which may not be a totally fair comparison to what it does going down the road but it would seem like it is running pretty much on the idle and transition circuits when under light load going down the road.

I then changed the Idle Air Bleeds on both carburetors per Quick Fuel recommendation.  Primary side of the carburetors went from 73 to 76 and the secondary side of the carburetors went from 33 t0 45.  This did make a difference in the idle O2 numbers and more so on the cruise test.  Idle O2 value went from high 10's and low 11's up to low 12's.  Cruise O2 values went from 11-11.5 up to 13+ under light load, this value was relatively stable from about 2000 to 2600.  It was very sensitive to throttle position, letting up on the throttle would drop it down to 12.0, giving it just a little throttle would lean it out for a short time, sometimes as high as 16, it would then settle back to the 13 range.  When on the cruise test increasing RPM above 2700 the O2 values would start dropping off, I expect that would be due to the main fuel system coming into play.  Today I took it on about a 50 mile run on the freeway with about 15 miles of steady 80 MPH at about 3000 RPM, the O2 settled in right about 12.5 so it would appear I could still put some smaller main jets in the primary side,  they were 72, and are 68 now.  I was thinking of trying some 66 or 64 jets.  Also, thought I might do the primary carburetor rather than both carburetors.  Is this a reasonable thing to try?

The idle O2 values still seems a little rich but reasonable on the cruise test under light load.  Not really sure if I should just leave it alone or try to improve on it.  If I do make more changes would I go bigger yet on the idle air bleed or put some smaller idle feed restrictions in it.  It still drives decent and idles fine.  It might idle just a bit better and picked up a tiny bit of vacuum with the larger air bleeds.  Looking for suggestions on this.....

So now I have a question that I hope this group can educate me on.  I have not had a lot of experience working on carburetors (until just recently anyhow) so I have been doing a lot of reading on these types of carburetors trying to gain an understanding of just exactly how they work.  Most of the material I have studied is based off Ford shop manuals for Ford and Holley carburetors. I also have one of Vizards book on Holley's that I think it would apply very closely the Quick Fuel carburetors that I am dealing with.  My question is about the idle and transition circuits.  The old 352 and 390 engines with 2 barrel carburetors have the same type of idle and transition circuits that work the same way, except they just have 2.  A single 4 barrel has 4 idle circuits, with mixture adjustments on the primary barrels only.  Two 4 barrels are double of the single 4 barrel.  So now there is 8 idle circuits sucking fuel while idling and in the transition circuits with 15-18" of vacuum.  How is a reasonable fuel mixture and O2 value obtained with 8 circuits sucking fuel?  Maybe part of the answer is the 2 barrel carburetor idle air bleeds and idle feed restrictions are sized way different but that is something I didn't have access too.  It just seems to me with 15-18" of vacuum and 8 fuel circuits it is almost a no brainer that it is going to be on the rich side.  I kind of debated even asking this question because when you give me the answer it might appear to be a stupid question but according to my wife, a retired 911 dispatcher, there are no stupid questions,  just a lot of stupid people.....

Thanks for all the feedback already given.

[Barry_R]

The short and brutally oversimplified answer is that yes - you do have eight circuits working.  But the carbs are designed for that - on a four barrel with non-adjustable secondary idle the circuitry is specifically designed to have minimal idle activity in the rear and most in the front where it can be adjusted.

[Joe-JDC]

You spoke of the idle transfer slots not showing in the secondaries, and that is the start of all adjustments needed.  It is basic to getting a Holley to idle properly, and transition to speed.  The Holley manual states that the secondaries need a .020" slot showing with the primaries closed.  Then you adjust the idle bleed screws, idle speed, and accelerator shot arm.  For dual carbs, you might have to close the slots to ~.012-.016" to get the idle speed down, but is will work if you close the primary blades and back off the idle set screw for accelerator rod/cable.  Joe-JDC.

[The Real McCoy]

Barry
I guess I looked at the idle air bleeds and idle feed restrictions (original specs) being 73/33 on the primary and 33/40 on the secondary and surmised the secondary idle circuits were contributing to the rich condition.  How is it they limit the idle activity on the rear?  I had thought that when I had turned the idle screws in all the way, with some improvement in O2 values, it was possibly just feeding of the secondary idle circuits and it was still generally rich.

Joe,
I do recognize that the transition slots are not showing on the secondary's, if they show at all the idle RPM is well over a 1000. Even on the primary side they are barely visible.  Barry had commented on earlier post that it will get air from throttle blade circumference which these carbs have a lot of.  Maybe I'm missing your point and apologize if that is the case.  As far as idling, transitioning from idle and general drivability I'm really not having any issues, it is the rich air fuel mixture that I'm really trying to address.

Thanks to both for your feedback.

[Joe-JDC]

The first step in adjusting any Holley after centering the blades is to set the idle transfer slot in the secondary.  Nothing else will fix the problem.  Everything else you do is a "band-aid" until you set those.  Joe-JDC 

[Barry_R]

Joe is exactly correct.  Since you cannot "adjust" the idle circuit on the secondary side of the carb, you need to make certain that the secondary blades are properly centered and the stop/blade position/transfer slot exposure is correct before moving forward.  That sets the baseline for the more readily altered primary side.

[The Real McCoy]

Pulled the carbs back off this morning and set the transition slot to .020 exposure on the secondary throttle plates.  This did move the throttle plate quite a bit to obtain the .020 exposure.  The primary throttle plates speed adjusting screws on both carbs were turned in until they began to open and then backed off until they were to full closed. The transition slot is not exposed on the primary side of the carburetors.  Idle mixture screws for both carbs were set to 1/2 turn out.

Started the engine up and O2 sensor now was reading in the 15-16 range so that did make a big difference.  I might not fully understand what exposing the transition slot accomplishes but expect it is an additional air bleed for the idle circuit with the throttle plate almost closed.  Now the problem is the engine is running at 2000 RPM,  probably due to the secondary throttle plates being partially open.  I backed the each of the secondary throttle plate speed adjusting screws out about a half turn to get it down to 1500 but of course the O2 sensor is now going low again.  I would expect that the 1/2 turn back out pretty much covered the transition slot again......

Any suggestions?

[Joe-JDC]

Since you are using two carburetors, you will need less slot showing in the secondaries.  I thought I had in an earlier post to set them~.012-.016" each.  If not, then I should have for two carbs.  The wider the slot is exposed, the higher the idle speed, so if you want to bring the speed down, slowly take the same amount out of each secondary blade position, and you can bring the idle down to 700 rpms.  Every set of carbs is unique, so you may find to get the best idle quality your secondaries slot will only be .010" each for final adjustment.  However, both carb primary blades should be closed and then just tweaked enough open to keep them from sticking in the venturi, and the idles screws in the metering block may need to be adjusted out a turn, or less.  Joe-JDC

[The Real McCoy]

You are correct. You posted .012 to .016 on dual carbs.  I just had the .020 in my head when I set them. I backed it off about a half turn on each but only brought it to just under 1500!and O2 was going back down so I stopped. Was really afraid I'm getting back to where I started from. I'll take another run at it tomorrow. Probably will pull at least one carb off to see if it's covered up or not.

Thank you for the help.

[427LX]

Are you running any kind of PCV system? If so you could put a restriction in the vac. feed hose to cut back on idle air flow from it allowing you to correct the idle speed.
Initial Advance Timing...if say you are running 14 degrees you could retard it to 12 degrees,slowing idle speed,and add it back in the advance curve.

[Drew Pojedinec]

or just disconnect the pcv temporarily to check if it has a large impact.

I ended up putting a piece of hose into my pcv line to slow flow a lil.  Took a bit of fiddling, and a solid 3-4 times of taking the carbs on and off to get them dialed in, keep the faith, you'll get it.

I'd also make 110% sure you have NO vacuum leak (sure easy to do with 2 carbs).  Even a tiny leak will destroy your ability to get it tuned. 

good luck

[The Real McCoy]

427 LX....

Yes I am running a PCV system, valve cover to back of intake.  Will consider trying your suggestion.

Timing currently at 12 BTDC plus vacuum advance connected to manifold vacuum so it has a bit of advance at idle.  Starts good at 12 when hot and water temp stays down when idling for long periods with vacuum advance active so I would rather not make changes unless I have too.

Thanks for the ideas.

[Drew Pojedinec]

The vacuum advancing the timing at idle would raise the rpm, no?

[Barry_R]

Restricting PCV is a really valuable suggestion.  You can drop to a .060 restriction in the hose and still have enough flow to keep the benefits of the PCV.

[My427stang]

Are the primaries fully closed even with it at 1500 rpm?

If they are, then IMO, it's getting air from somewhere it shouldn't

[The Real McCoy]

I'm going to go back at it this morning to verify secondary throttle plate to transition slot location and set them to .010 so I know exactly where I'm starting from.

Drew
Think I'm good on no vacuum leaks.  I do have phenolic spacers that I had to machine down to get the hood/air cleaner/distributor to play together.  The machining of the phenolic was not really a perfect mirror finish so I used gasket sealant to glue both carb gaskets to the spacer.  Intake is an NOS low riser and of course carbs are new.  Carb ported fitting is plugged and carb manifold vacuum port goes to distributor and Snap On vacuum gauge that has kind of become a permanent fixture.  All new hoses and tight.  The wild card is the PCV which I will address this morning.  It has always maintained relatively good vacuum, little less than 15" when idle was 800-900 and probably 16-17" at 1000 as I remember.

Yes RPM did jump a bit when I switched to manifold vacuum advance.  I got caught up in a couple of traffic jams and water temp would go right up to the Hot mark in about 15 minutes.  Not really to the danger point but I really didn't like looking at it.  Changing to manifold vacuum really settled it down, at least on my car it seemed to make a big difference, so I would like to keep it that way.

Barry,
Yes, thought the same thing about the PCV, that is a really good idea to block off/restrict.  Will be the first thing I try when I get the carbs back on and I establish where I'm at with .010 on the secondary plates.  Is there a target vacuum/pressure that is desired for the crankcase?  It wouldn't be that hard to put port for a magnehelic gauge on the intake breather cover.

Ross,
Good point about extra air...., hindsight is I remember when on the dyno it really would not idle down.  Time was limited so the issue was not pursued at that time but that's another whole story in itself.  In the car with open headers it was running fast I think we backed off the secondary's to get it to idle.  More hindsight is the O2 numbers on the dyno were not as rich as I am seeing now once I added the O2 sensor, probably because of closing the secondary's. The primary plates are fully closed.  I'm really hoping the PCV idea has a big effect on the problem.  I guess my big worry is the secondary throttle plates really start moving when uncovering the transition slot.

Again, thank you for all the ideas.

[The Real McCoy]

This is what I'm seeing after setting the transition slots to .010 exposure on the secondary's and getting the engine fully warmed up.  Ambient temperature 59F, elevation 1310 feet, humidity 91%, and barometric pressure 29.97 if anyone is wondering. 

RPM                O2 Sensor             Vacuum
2000                 12.9-13.2                20.5"
Pulled PCV from Valve Cover and covered with piece of stiff plastic.
2000                 13.0-13.2                20.5"    Really didn't seem to have much effect at this RPM, darn......
Back each secondary throttle stop set screw out about 1/8 turn
1900                 13.2-13.6                20.2"
Back out another 1/8 turn on throttle stops.
1775                 12.8-13.0                20"    I would guess the transition slots are covered by now.
Back out another 1/8 turn on throttle stops.
1625                 12.6-12.7                19.8"
Back out another 1/8 turn on throttle stops.
1400                 12.3-12.4                19.3"
Uncover PCV  (hanging out in the breeze)
1450                 13.3-13.4                19"
Plug PCV back into valve cover  (opposite valve cover has twist in vented oil fill cap without fitting to air clearer)
1450                 12.9-13.2                19"
Put it in gear and let the clutch out when I shut it off, pretty sure it would have made an attempt to keep going at 1450 RPM.....

Flaws in my data.....
1/8 turn out is kind of a judgment call, may not be exact but think I was close.  I tried very hard to turn each set screw the same amount.
Vacuum gauge readings are not exact, gauge is steady but It doesn't read in .1 increments, my best interpretation that there was a change.
O2 sensor moves around a bit and I tried to capture the general range it was mostly displaying.

I am sure if I continue to back out the secondary throttle stops I can get it down to 800 RPM with 13-14" vacuum, at a 1000+ it will do 16+".  Problem is I'm back to the rich condition I'm trying to address.  How do those vacuum readings sound at those RPM's?  I guess I thought they were reasonable.

I know Ross felt it was getting to much air at the 1500 RPM which I agree with, I think it is too much opening on the secondary's and not from some other leak point.  Primary throttle is definitely closed.  Any other thoughts on where it could be getting air from....   If I did have some other vacuum leak would it show up more on the vacuum gauge or do these numbers indicate no leaks?  I did take a close look at the carb gaskets, spacers and base plate today and didn't see no issues.  Intake gaskets I think can be ruled out as a cause, not burning oil or other symptoms typical of an intake leak.  The only other fitting on it is for the PCV at the back of the intake, I did look at the fitting and PCV hoses, no issues observed.

So, I guess I will go out and ponder what I might be missing and hope one of you will give me another idea to pursue. 

Thanks for bearing with me on this.

[My427stang]

So, I am in NO WAY saying Barry or Joe are incorrect, however, I do this a lot differently and haven't seen the issues you are seeing

I start with the rear barrels just off of touching, basically the only thing I care about is that the butterflies can't bind in the baseplate

Then I put the primaries at .020-.030 transfer slot showing.  To be honest, I start with them looking "square" with the choke either adjusted open, or verified not touching

Then I start it and see where I am.  If I can get idle high enough without getting into the transition slots much more, I adjust to best idle, equalizing the front and back sets of primaries

So, all of that it sounded like you did, and then it was running rich by the O2 sensor at idle, and that's what brought you to the original question

so............

1 - If you can bottom all 4 primary adjusters after doing what I said above, and it doesn't stall or it idles fine and still rich, then either the secondary idle circuit has something wrong with it (too large IFR on the secondaries, NO IFR, warped body, or something else, because at that point (primary adjusters closed and rear butterflies closed) you should not have enough fuel to idle, nevermind idle rich

2 - You are sitting on the choke mechanism and didn't realize it, so the primaries are really open.

3 - Is there any chance you have an ignition problem?

In the end, I have never had to chase the secondaries other than to allow me to close the primaries on a good set of carbs.

One last comment, I have seen bad carbs from every manufacturer out there, QFT included.  Odds that two carbs have issues are unlikely, but remember, you can always swap one or both with a loaner and see how the car does

[Joe-JDC]

If these are reverse idle carbs, then all this information is suspect.  They lean out the further you screw out the idle screws.  I have never had a carb that liked setting the idle with the primaries.  It goes against everything I have learned over the last 50+ years dealing with Holleys.  JMO, but I can be wrong on occasion.  Joe-JDC

[My427stang]

So only 30 years of experience here...and I can't gain on Joe, every year I get one, he gets another one too

However, just teasing Joe, but I am a bit stumped on the situation.  All 4 blades on each carb are closed, except secondaries are just open enough to show .010 of the rear transition slot and it won't idle under 1400?  Something is goofy, did someone drill holes in the butterflies? 

If yes, find that guy and kick him in the nads LOL then put a dab of JB weld over every hole, it'll last forever

If no, maybe the way you are measuring ".010" is wrong?  An engine needs air and fuel to run, and if you have all the blades shut down, it shouldn't be humping away that high.

I have to admit, I tend to be suspect of idle a/f  using an a/f meter/O2 sensor, does it run well?  Does the carb adjust normally?  Have you run it to get the exhaust good and hot and then looked at idle a/f? 

[Drew Pojedinec]

Think I'm good on no vacuum leaks.  I do have phenolic spacers

I got caught up in a couple of traffic jams and water temp would go right up to the Hot mark in about 15 minutes.  Not really to the danger point but I really didn't like looking at it.

Just a few thoughts, and forgive me if this seems basic, I do not ever mean to appear condescending.

-Get a real water temp gauge, a reading of "hot" on a factory gauge doesn't really mean anything unless the engine is boiling over.
-Oddly my super nice phenolic spacers WERE my vacuum leaks.  Seems odd, and I've never had a problem with any other spacers.  I tried everything but couldn't ever get them to work right.
-You are aware you can adjust the secondaries on a Quickfuel carburetor without removing the carburetor, right?  It takes a small allen wrench, and yes it's a little difficult on a hot engine, or with mine that has a lil cam and it shakes around a bit.

Good luck, keep at it, it's worth it!
Drew

[The Real McCoy]

No holes in butterflies that I noticed.  These are new carbs but will recheck next time there off.  Probably be in a few minutes.

As far as how I measured the .010 transition slot exposure....., held the throttle against it's adjusting screw and actually used a .009 feeler gauge, held the gauge radius against the butterfly and bore radius and was just able to make out the edge of the slot above the gauge tip.

I did take it for a drive with the idle up high.  It was a little unresponsive and touchy to get going (it does have 3.00:1 gears) which was kind of out of character for it and O2 sensor on cruise light throttle was higher than I'd seen on it, in the 15-17 range.  Backed the secondary throttle screws out together to get the idle back to 800-1000 and it drove better and O2 come back down so expect the open secondary's were causing the previous characteristics.

Carb adjustment via mixture screws have not been real successful.  If you want to wade through the whole post there is some description of what effect they had early in the post.

Took it out for 50 mile run the other day on the freeway, more description on this about mid post.

Ignition problem....., starts and runs good.  Spark from the coil jumps a good 1/2".  I can't say it is fat and blue but is mostly blue in the daylight anyhow.  Distributor and coil are new Pertronix with the engine.

I know it's hard to fully comprehend without seeing it in person but it seems to me the butterflies have to move an awful lot to expose the transition slots on the secondary's.  You guys might be able to tell immediately if this is normal or not.  I have no background to make an accurate judgment other than I think they move a lot and the RPM is very high when the slots are exposed.

Haven't really tried this on the primary's but will probably try Ross's suggested method and see what they do.

Just seen Drew's post...
Yes, am aware of the allen screw.  Actually getting pretty good at doing it on a hot engine.

Did you figure out how/where your spacers were leaking.  I'm still fairly comfortable with the ones on mine but don't want to discount them.

[Drew Pojedinec]

Did you figure out how/where your spacers were leaking.  I'm still fairly comfortable with the ones on mine but don't want to discount them.

No, but they did leak fuel *through* them.  These were fancy Canton spacers, not just summit name brand.  I'm going to guess they were just really porous.  I had the issue, took them out, put carbs on, no issue.... put different spacers on, no issue.  This was after installing and reinstalling a few times, even greasing the gaskets, etc trying to get them to seal up.
I quit messing with them and used some other spacers I had hanging on the wall and had no further issues.
Wasn't a huge leak, but the difference between 8.5 and 10inches of vacuum made it nearly impossible to get the engine running perfectly.

[My427stang]

First I am sorry I didn't read the whole thing the first time, so I am going to play the quote game and make some comments

The engine runs and drives reasonably well other than the black exhaust. 

I recently added a wide band oxygen sensor which verified it is running rich, at idle it was reading 10.9 to 11.4. 

Going down the road at cruise speed it pretty much stayed between 11 to 11.5 from 2000 to 2800 RPM. 

Coasting only got it up to 11.6. 

The Idle Mixture screws do not seem to be able to lean it out when idling. 

I even turned them all the way in and it only come up to 11.7 t0 12.0. 

Road testing with them screwed all the way in netted about the same during the cruise test 11.7 to 12.0. 

The first thing I would think of when reading this is BAD power valve, not wrong, but leaking.  Fuel would travel into the cavity behind it and be rich at all times.  The fact it has always idled with the screws buried and it is rich in all circuits and at all times  makes me think "internal leak" 

If not the PV, maybe an overzealous tightening of the bowl screws warped the body and causing cross channelling?

Maybe the wrong gasket somewhere inside?  Porous metering block?

I also like the idea earlier of a plugged bleed but that would be after I ruled out the other things. An air bleed emulsifies the fuel as well as timing it.  When one is plugged the circuit starts immediately with pure liquid fuel. 

I would NOT be blaming transfer slot / throttle position settings with it being pig rich everywhere, if it was, it'd be cleaning up somewhere

If it were me, I'd look behind both PVs to see if its wet, if it's wet behind one in the body of the carb, that's likely your guy.  If you don't see it, have them both checked or just replace them, but I'd likely go 6.5s with all your vacuum, but the 5.5s should work fine too.  If you find something, I'd likely put the carbs back to "as delivered" and see where you are

[The Real McCoy]

Just put the carbs back on after setting them up with the Primary transfer slots exposed and the secondary fully closed.

I do want to throw one observation out there for comment.....
I checked the position of the throttle plates when fully closed and again when the transfer slots just became visible for both primary and secondary on both carbs.  When I did this I measured the distance of travel with a caliper from full closed to the transfer slots just being visible.  This measurement was taken 90 degrees from the throttle shaft on the edge of the throttle plate that tips up into the carb venture area as it opens.

Movement from full closed to transfer slot just visible was as follows....
Front carb Primary .019
Front carb Secondary .066
Rear carb Primary .020
Rear carb Secondary .070

That might be why I think the secondary throttle plate is moving a lot before the transition slot exposes.  I guess I'm wondering if this is as designed or could be an issue.

Ross, will need to carefully read your comments and review as needed.

Just got orders to wash the gasoline off and go for dinner.......

[My427stang]

Just got orders to wash the gasoline off and go for dinner.......

That's funny, same happened to me, but the order was "man the grill"

[e philpott]

I'm running dual 600 1850's but my car wouldn't idle down with the secondary showing the transfer slot either , I had to close them up but not binding to get the idle down to normal ......

[The Real McCoy]

Drove the car for about 30 miles when we went for dinner with the carbs set up per Ross's suggestion.  It seems to run fine but think the O2 readings are about the same.  My copilot was not writing the information down so I don't want to post any numbers until I'm sure on that.  Will have to take it out again and document.

Ross, regarding your comments on you 5:16PM post......

I think the constant richness being described has to do with the idle and transition circuit being active until the main fuel system comes on at much higher RPM.  There is more comments about this later in the post.  I did change the idle air bleeds and it did show some improvement for idle and the cruise test.  That being said I did have the bowls off and changed the main jets from 72 to 68.  At that time I did not notice any fuel behind the power valve, but, I wasn't really looking for that.  So, I'll probably unzip the carbs again and double check that.

Warped part/over tightened bolts...... I hope not, these are new carbs and I feel I have been very gentle with them.  Bolts are snug but I have not carried away when tightening them.

Porous metering block/wrong gasket.....Hope not on this too.  This cowboy is going to have to get a lot smarter or get more local help to ID that.

Transfer slot/throttle position...... you know I don't fully grasp what this does or how critical it is to air/fuel mixture values for the idle and transition circuits.  It seems to me it is an additional air bleed when exposed with the throttle plate mostly closed and turns into an additional source for an air/fuel mixture as the throttle plate opens. I also don't understand if it is more critical for the secondary side of the carb compared to the primary side.  I think that was Joe's point early in this post that I had to get the secondary set correctly, and, I think it did have a positive effect but then I got in to the really high idle speed. 

So, does anyone have an opinion on the extra .050 movement of the secondary throttle plate compared to the primary to expose the transition slot?  It would seem that this would explain all the air for the high idle speed when the secondary transition slot is exposed.  I do have an old Holley, I think off a 66 390 GT, to compare to the Quick Fuels.  I did not measure the Holley but the movement is very minimal on the secondary throttle plate to expose the  transition slot. 

I am leaving this morning and will be gone until Wednesday PM so will not be able to work on the car until then.

Appreciate all the idea's and help.

[My427stang]

Ross, regarding your comments on you 5:16PM post......

I think the constant richness being described has to do with the idle and transition circuit being active until the main fuel system comes on at much higher RPM.  There is more comments about this later in the post.  I did change the idle air bleeds and it did show some improvement for idle and the cruise test.  That being said I did have the bowls off and changed the main jets from 72 to 68.  At that time I did not notice any fuel behind the power valve, but, I wasn't really looking for that.  So, I'll probably unzip the carbs again and double check that.

Appreciate all the idea's and help.

So here is why I do not agree.

Every carb, every time, has the transfer slots and the idle circuit feeding the mixture when boosters come on line.  In fact, for the main jets and PV to come on line, the blades HAVE to be open enough to have airflow across the boosters, otherise they wouldn't function

So, if you were rich at very low RPM and then it cleaned up, I would say you "may" have a transition slot (or IFR) issue, but even then, I don't really think so, just trying to find logic to support your effort. 

Also remember, the .033 IFR feeds the idle and the transition slot, compare that to the .065-ish and .055-ish sizes of the jets and PVCR.  You have to calculate area of each to compare, but the area of a circle RUNS AWAY in size as the diameter gets bigger, so that IFR size really is tiny once the boosters come on line.  It's effects should change, but they are almost staying constant.  In fact, when you close down the idle circuit, you had very little change, which tells me the fuel is coming from somewhere else other than the shared idle/transition feed

So, I'll take a knee and throw out another comment.  Maybe your a/f meter is inaccurate if the engine is running well?  Just a thought

Back to it though, in order for something to be rich the entire time, by a significant amount, I don't think it can be a transition issue. 

Also, I need to say this again.  Do not look at air bleeds as a/f adjusters.  Look at them as froth makers that set that circuit's timing and response

Idle air bleed
- Feeds the IFR, which feeds both transition and idle.  Takes liquid fuel and mixes it with air to make it frothy (emulsified) so it's easily atomized
- Times (determines how quick it responds) to each circuit (think of how hard to suck soda through a straw with a hole)  more hole, takes longer and more pull to get your root beer
-
HSAB
- Same thing, but has more inputs.  Kill bleeds in metering block, booster design, etc.

So digest all of this for a moment, I am going to calculate the percentage of IFR area to jet, then jet plus PVCR to show you.

Also, remember again, if you had a bad PV gasket, or bad PV, it lets the fuel get to the engine WITHOUT going through the boosters.  It basically drips all the time and is sucked out of a chamber behind the PV that is supposed to be dry.  I think if you are going to trust your numbers, you HAVE to check the PVs

This is not to scale by any means, but again, shows that once the main jet comes on line, if it was an IFR/transition slot issue, you should start to clean up significantly with RPM, especially with the jet drop

[My427stang]

Math geek is back......

I did some quick calcs, and realize I am jumping in and out of this without comparing it to all your numbers that you reported

However, considering one barrel of the carb with a .033 IFR (area of .00085 sq in), one jet for that barrel with an area .00376 sq in , and one PVCR of .055 with an area of .00238 sq in, you can already see, that transition slot contributes MUCH less to the math problem than the mains

.00085 vs .00376 (and at times add .00238 for the PVCR) (note the zeros)

Of course you cannot just calculate area of a fuel restrictor to talk about contribution at different times and throttle positions, but if you consider the chart above, you get fuel in the following order: idle fuel, then add transition fuel as you crack the throttle, then add main AND PVCR under load, then it should return to just main jet plus idle/transition as vacuum comes up

Initially, if I did the math right, and assuming a perfect signal to all circuits, the idle and transition would contribute 12% of fuel under load with throttles wide open, then clean up to 18% of fuel with no PV.  My key point is, your constant-ish 12:1 doesn't make sense to me for a transition circuit issue, it wouldn't stay constant like that  Not to mention you have adjusted the positions 5 ways to Sunday already

That math of course assumes the IFR is feeding full fuel through both the idle and transition circuits, however, you were still rich when you shut the idle down by closing the primaries.  Hard to imagine how much more the transition will pull with the idles crews closed, but you'd expect SOME reduction in the combination even though the transition circuit may pull a little more if idle is shut down (the problem is, in that case it shouldn't idle though, and yours does)

If I simplify the entire issue, pretty much you have been seeing 12:1 consistently with the original carb, as originally set up.  To me, if the problem was too much transition fuel, you'd expect the engine to get leaner as the main and PV circuits came on line (and if just happened the PVCRs are too big too, it would at least lean out at cruise).  Unless of course the mains and PVCR were exactly, perfectly too rich too, but you did a jet change and it didn't change dramatically so I think that rules that out

The more I read what I type, I still think the following are possibilities

1 - It is so rich due to an internal leak that the O2 sensor is maxed so you aren't seeing improvements because the tool doesn't have the fidelity, or the O2 sensor is just incorrect
2 - If it is really rich on all circuits, it is either one or more PVs are blown, the PV gasket is leaking, or you have internal cross channeling and/or porosity

I see you are traveling, but when you get back, maybe pull the plugs and see some color?  It's hard to see color nowadays, but I think 12:1 would show something, even if it's only shiny porcelain

Another option, although to me it's a bit overkill, is to pull a carb, block the manifold with a flat plate.  See if you can clean up idle with one carb, especially making the idle screws work well, then swap it for the other.  Or if you have a buddy with a single carb engine, try both on his.  You may find one carb alone is the issue

[My427stang]

Transfer slot/throttle position...... you know I don't fully grasp what this does or how critical it is to air/fuel mixture values for the idle and transition circuits.  It seems to me it is an additional air bleed when exposed with the throttle plate mostly closed and turns into an additional source for an air/fuel mixture as the throttle plate opens.

I know I am blowing up the posts, but just noticed this comment

The air bleed does NOT function as an air jet and you should not consider it a source for air

During idle - air comes from around the throttle plates, and the IFR+IAB feeds gas/air froth.  If there is no IAB, it comes out as raw fuel and is tough to atomize, but air would still be there from throttle position

During transition, same thing...the transition circuit is there BECAUSE of more air coming due to what the drivers foot is doing.  With big foot movements, the accel pump helps out, but small movements, the frothy fuel atomizes with the air coming around the butterflies so it can stay in suspension

So don't think about air bleeds as air jets, true, some air has to be added to the mix during emulsification, but nowhere near what is coming around those big throttle plates.  The bleed is there to emulsify and determine how quickly that circuit responds to changes

[The Real McCoy]

Wow Ross.... It looks like you just over whelmed me with logic and facts. Probably all good stuff.  Give me sometime to sort through it. Hope to have it digested before I get back on Wednesday.

Thank You.

[My427stang]

Sorry brother, wife and daughter were sleeping in, I was on second cup of coffee

[Falcon67]

>My copilot was not writing the information down

For this kind of work, you'd be better off with something like an LC-1 and a laptop, or LC-1, a 4 channel DMP and the pocket logger.  Reading a gauge for tuning is going to be hit-and-miss IMHO.  I hook up my LC-1, drop an old XP laptop in the passenger seat and do whatever, then sit at the bench and play back the log to see what's going on where. 

[427LX]

Concerning your high idle speed issue.... Since you are running manifold vac. to the vac. advance, how much is the advance gaining at idle over your base setting at the crank... you have 12 at the crank with vac. plugged and it jumps to what at idle when plugged in?
Another little item... on my setup I'm running the weakest secondary spring,White spring in both carbs...engine loves it!
However on getting my engine to a steady 1000 RPM hot idle,I noticed just a bit of slack in the rear carb secondary link to primary throttle. Under Idle or cruise conditions this would allow the secondary throttle plates to crack open a bit more raising the idle speed.
Solution was to slightly bend the link open to take up any slack but without binding the secondary movement.
Seemed to fix that problem.
Another idea I haven't tried..maybe a switched PCV vac. feed that would block the PCV Vac. at curb idle then when throttle is open during cruise speeds the switch is open allowing full PCV flow.
Good reason I haven't tried that...I don't run vac. advance!

[Cyclone03]

I'll admit I stopped reading when the IAB change moved you in the right dirrection.
Put the as delivered IAB back in and start leaning the IFR's.

With 2 carbs you have the potential to dump a lot of fuel at light load/cruise. You can drop the IFR .001" at a time but I think you will end up in the .026 range on the primary side. .028,.030 secondary. IAB v.IFR is about 3:1 a .073-.070 IAB change is like a .033-.032 IFR change. But the IAB really  tunes WHEN the transfer system starts and stops it really does move the point it works,and you can see it with an O2 indicator,tach and vacuum gauge in back to back testing.   

I may have missed  it,are the carbs 4 hole idle?

If it's primary only,2 hole, try to get the mixture screw out 1 turn  at idle ,if you find it just stumbling right off idle when you drive it turn the mixture screws IN 1/4 turn,if it gets better make the IFR bigger ,by .002.

As Ross's chart shows you will find yourself driving around in the transition area the most,with dual quads you may not pull into the mains at all until 3000rmp and 80mph.

Being you have so much fuel flow available I think your secondary will "just" show the transition slot,call it barely opened,you dont want the blade sealing the bore closed. work on getting the primary at the "optimum" .020 or square slot shape. You want good strong transfer fuel flow just off idle.

When you get the IFR right you will see idle O2 AFR changes with 1/4 turn of the mixture screws. Work to have all the mixture screw set at the same point out also,when setting start at a base,say one out,then turn each in 1/4,continue around 1/4 turn at a time at some point the idle rpm should drop if it starts running rough but doesnt die at full closed lean the IFR. You may (most likely) find when you lean the IFR to the point you can kill it the transition is too lean,go back up on the IFR .001 and call it good enough because the drivability is more important ,work the mixture screws to clean up the transition.

It really is a back and forth process .

In tuning a Demon 850 on my stroker 390 I put 90 mains in all four corners so I knew when the mains came in and found with a 3.70 rear gear in 4th gear 1:1 I didn't see any AFR change until 3500rpm and over 1/3 throttle, had to get the vacuum in the 8-10in range .
In OD the load went up so the turn on point was much lower at 2600rpm but still 8-10in vacuum. In normal cruise driving as high as 70 mph a big carb,or two, works in the transition zone almost 100%.

I will say with my above test the mains do pull at mid to high engine load,call it more than just tipping it.
Sometimes a test brings clarity and can help you understand the carb circuit you are working in.

Focus on one circuit at a time to get the best drive-ability.

[The Real McCoy]

Cyclone03

Thanks for the feedback.  You make some good points that match up with what my engine seems to be doing, especially being on the idle and transition circuit while going down the road.  Ross has also been a huge help on this.  I have been sidetracked by other things going on so have not been able to devote a ton of time to this.  I will get some IFR's coming and go with your recommendation.  Probably will take some time to get the IFR's and get them in but will post results when it does happen.

Carbs only have mixture screws on Primary side.

[The Real McCoy]

Just an update......

I ended up ordering some .025 and .028 IFR's for the primary side.  Seems that QF has .020, .025, and beginning with .028 they start in .001 increments on IFR's.  (Secondary IFR's are .040 and are part of metering plates so did not make them smaller). 

I changed the IFR's from the original .033 to .025 and the IAB's from .076 back to the original .073.  The secondary IFR's are still .040 (original) and IAB's are .045 (QF's initial recommended change from .033 to .045).

The above change made some progress bringing the cruise O2 reading up to about 13 and idle about 12.  It sometimes will drop down to the 10.5 to 11 at idle and noticeably load up but usually work it's way back up to 12 if it is left idling for a few minutes.  It will also sometimes lean out a lot, to 20+ while driving a round town at low speeds with light throttle, giving it just a little throttle will bring it back down quickly.  I put about 300 miles on it over the weekend and O2 readings were very stable around 13 going down the road at 2000 to 2400, this was a definite improvement but still a bit rich.  It did pickup at least 2 MPG over any previous MPG data, I do record miles and gallons when ever I fuel up.  The best before was maybe 11, usually between 10 and 11.  The trip to where we went on 2 lane roads, 55-65MPH netted 13.3 MPG.

So moving on to the rest of story....., during this whole ordeal I have noticed raw gasoline in the vacuum lines when disconnecting them.  Wasn't really sure if it was in the ported line or the manifold vacuum line until just recently but it appears to be the ported line based off recent observations.  I have about a 6" vacuum hose stub with a nipple union for each port which goes to the ported and manifold vacuum nipple on the throttle base plate of the primary carb.  I have also noticed plenty of gasoline under the carburetors after they have been removed during some of the recent exercises with the carburetors. It is very common for raw fuel to be puddled up in the primary bore of the intake after the carbs are removed.  One day after the primary (front) carb had been off overnight I measured how much fuel was in the front and the  back bowl.  I got approximately 7/8 ounce from the front bowl and 2 3/4 ounce from the rear bowl. 

Last night when we got home I immediately pulled the carbs off and set both carbs up on blocks on the garage floor so they were level.  It wasn't long  before there was a puddle under the rear carb.  The front carb took a little longer but it started dripping gas out of the ported 6" stub vacuum line.  It's puddling of the gasoline was not as sudden nor as severe as the rear carb, it only puddled under at the vacuum hose and not under the carb. I guess I can't say if the leaks are actually from different leak points or not.  The rear carb does not have vacuum ports to set them up the same way.

 This morning I measured the fuel in each bowl, the carbs had been off the car for about 16.5 hours.

Front Carb                                                           Rear Carb
Primary Bowl 2 1/4 ounce                                     Primary Bowl 1 7/8 ounce
Secondary Bowl  3 1/8 ounce                                Secondary Bowl 3 1/4 ounce

This fuel leakage all seems to be internal.  There is no raw gasoline dripping externally on the carburetor or intake manifold, other than if the ported vacuum line is disconnected it will dribble a little out.

So I guess my questions are.....
1.  Is this fuel migration out of the primary bowls normal?
2.  If it is not normal what would the root cause be?
3.  If this fuel migration happens when it is not running, is it possibly the main reason for the rich conditions when it is running?

Appreciate any ideas on this.  Thanks

[The Real McCoy]

Hey 601 hp

You sent me an inquiry via PM back in early February as to what happened with my Quick Fuel carb problems.  I did not see the PM until a few days ago and responded via PM.  Check you PM and advise if you have any other questions.

Thanks.