2 x 4 Quick Fuel Carb Tuning

[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!