New Stroker Running Rough Daul Quad Quick Fuels on RPM Air Gap Final Answer

[Falcon67]

thoughts:

-Most engines seem to like the short yellow VS spring in a dual 600
-I rarely exceed 66 or 67 in primary jet in a 600cfm carb, I'd leave finding the lean limit in jetting until all the other issues are worked out.
-If you aren't totally redoing a carb and just changing jets, I don't see the need for an O2, seems lotsa folks chase their tails, paying more attention to a gauge than to how the engine is running.  Pull some plugs, make some guesses.

X2 on the O2.  Reference - with the dual Ed 600s that I run on the 302, the A/F from the Innovate interface was good, 13ish mostly and drove decent.  But to get best performance and MPH at the strip, drilled both shooters to .035 and went up 4% (Edelbrock one step) in fuel on both ends of both carbs.  O2 is a good tool, but you still have to try stuff.

Trans not shifting into 3rd well - that sounds like vacuum modulator, either you have really low vacuum in the intake or the hose/line has a leak. 

It does sound like carb(s) issue.  For fun, I have two same frankencarbs here - ProForm 750 DP centers, QFT blocks, billet 4 corner base plates, etc.  Same jetting, same IFR (33 IIRC), same PV.  Put one on the dragster - blubbers, breaks up at RPM, not the least bit smooth, sounds like it is loading up.  Swap on the other - clean idle, clean above 3000 (big solid roller in the motor).  Go figure.  Says to me that there is something really out of whack with one of the QFT blocks.  I have a ProForm purple block with the same deal - used it  as the front block on a 750, never worked well.  Changed to a stocker from another 750DP - ran well. 

[jayb]

Thank you for all of the feedback and input.

I do have a wide band installed, using it for reference to make sure things are not getting too far out of line.  A/F is generally sitting between 13 and 14 for most driving conditions, 12 for cold start and after letting off the throttle, up to 15 under hard acceleration.  It bounces around a bit at low RPM, due to the high overlap cam I am told.  Trying to stay on the slightly rich side of things all the time until I get it dialed in.

If your wideband is accurate you are running lean under hard acceleration.  You should be shooting for 12.5: to 13:1 at wide open throttle, from 3000 to 6000 RPM.  Sounds like you are way higher than that.  I'd bump the main jets up six sizes and run a few more wide open throttle tests.  Do it in a higher gear so that the wideband has a chance to settle down.  You might have to go even more than six jet sizes.  If I saw those numbers on the dyno I'd be fattening up the carbs a bunch.

[Drew Pojedinec]

You would adjust jet even if the cruise afr is ok? 
Or would you look at the PV opening point and pvcr size?

[Barry_R]

When tuning Holley accelerator pumps you have a LOT of variables to tinker with.

When you work with a "fixed" pump volume (like the "30cc" standard pump) and a single chosen pump cam, changing the pump shot orifice changes the amount of time that a squirt takes to deliver - it does not really change the amount of the fuel.  You will get +/-3cc of fuel provided in a short time or a longer time - a lot "right now" or a little over a longer period.

You can change the timing of that fuel and the available volume of fuel by using a different pump cam - some cams provide a longer stroke using more of the available pump capacity.  Obviously some of the cams provide more or less fuel at various points in the throttle rotation as well, and have two or three possible clocking locations relative to the throttle blades.

That spring on the pump arm will also mitigate the opening rate a bit when you slam the throttle open no matter how fast the cam tries to open.

What this means is that you can try to "fix" a problem by throwing a ton of fuel at it with a big shooter and either have it work - or end up with a rich hole followed by a lean hole as the throttle opens.  The only thing you can do is to buy the assortment of cams and a few shooters and try stuff.

Pump tuning is not really difficult - it just takes iterations until you are happy with the results.  As Drew said - do not fixate on the O2 numbers for acceleration behavior - work on getting it to run good.  That's what really counts.

[Barry_R]

You would adjust jet even if the cruise afr is ok? 
Or would you look at the PV opening point and pvcr size?

Darn near nobody ever does it that way - - but they SHOULD.  The PVCR is effectively a high load & WOT jet and gives you exactly what you desire - lean cruise and richer at WOT.  On some Dominators back in the proverbial day, they had the PVCR as large as the main jets and needed to run a low restriction power valve for them to deliver enough fuel.

[WerbyFord]

You would adjust jet even if the cruise afr is ok? 
Or would you look at the PV opening point and pvcr size?

Darn near nobody ever does it that way - - but they SHOULD.  The PVCR is effectively a high load & WOT jet and gives you exactly what you desire - lean cruise and richer at WOT.  On some Dominators back in the proverbial day, they had the PVCR as large as the main jets and needed to run a low restriction power valve for them to deliver enough fuel.

I do what Jay said while tuning, with the cheap old 4160 carbs I deal with, you can change the primary jets but the other stuff, once you drill it, its drilled. And if you drill the secondary "plate", you have to buy a new one which costs usually more than I paid for the whole carb. I know, I'm living in the past, I don't think I ever paid more than $35 for a 600 Holley (and that was a 390gt carb).

I agree that seems lean - as I stated above, I've seen two specs for the BJ/BK carbs. One has an .079" secondary hole, the other has a .064" hole which is of course way leaner. WAY leaner. If you have the "lean" spec BJ/BK, it may well be way too lean in the secondary. Again you could block the secondaries shut and see what the wideband says. You'll be down about 35hp but running on those pure 66 Jets and their PVCR's. That should be pretty close, unless you're running open headers.

[Thumperbird]

How stupid is this idea?  Be honest.
I have 2 50HP each nitrous plates installed, could I just activate the wet side fuel delivery for a quick blip of fuel while under hard acceleration and see how it behaves? 

I did not record it but I think the AF went from just shy of 15 when it was struggling under 5000 rpm's to just north of 14 when it smoothed out quite a bit over 5000, nothing is calibrated here so just relative info. at best.  I asked Carl's Ford for a build rundown (2nd request) on the carbs and will figure out best way to optimize AF at full throttle.

The thing overall is a gas pig so if i can do it without running rich all the time that would be best.

Thanks. 

[Thumperbird]

Not sure how many people are running Holleys on the Edelbrock dual manifold.
Is it possible that this combo. is just more thirsty or behaves somewhat different than other dual carb/intake combos or a single on an RPM air gap?  Or am I just dealing with typical setup issues?

Can anyone chime in on variation they saw running a single Holley on the single Edelbrock air gap as opposed to single Holley on other similar manifolds?

I know the duals present a whole new picture but wonder if there are any correlations to what I am seeing in the single carb. world for various intakes, i.e. the need for lots more fuel on the top end for the air gap on an otherwise middle of the road 445 stroker?

Heavy car playing into this combined with a wide ratio C6 giving me some unique challenges until the thing really opens up?

[jayb]

How stupid is this idea?  Be honest.
I have 2 50HP each nitrous plates installed, could I just activate the wet side fuel delivery for a quick blip of fuel while under hard acceleration and see how it behaves? 

It's pretty stupid    Just kidding, but activating those plates on the fuel side would give you way, way too much extra fuel...

[Barry_R]

Not sure how many people are running Holleys on the Edelbrock dual manifold.

The answer to this question is probably "one" - and its "you".

Those wide angled spacers are introducing a wild card variable that nobody has worked with...

[andyf]

Not sure how many people are running Holleys on the Edelbrock dual manifold.

The answer to this question is probably "one" - and its "you".

Those wide angled spacers are introducing a wild card variable that nobody has worked with...

Sometimes the weird stuff doesn't work. I've built plenty of weird stuff over the years that didn't work so I'm familiar with the drill.

[WerbyFord]

These guys (below) have some good points.
I looked in the Gonkulator database at all the Edel 8v RPM intakes I have in there - nobody running Holleys, all AFB-style.

I have seen a phenomenon maybe like "Wind Shear" in intake design - I designed a home-made "Trips" intake for a straight-six a while back. It did funny stuff at high rpm (high means near 4000 here) - started to go flat, skip and miss -  throttle plates of the added carbs too close to a wind shear area. I was able to make it go away but it took some redesign. Maybe something like that going on in the spacers?

A way to find out: Why not try a couple Edel/Carter AFB or AVS carbs on there, without the spacers. In my experience, twin Holleys will outrun twin AFB's by 1-2 carlengths, but so what? The twin AFB's still run good, smooth, right up to the top. It could help isolate the problem.

But first I'd block those secondaries shut and try it. Then pull em off and see what secondary "jets" (holes) are in there.

************************************************************************************************
Barry R:
The answer to this question is probably "one" - and its "you".

Those wide angled spacers are introducing a wild card variable that nobody has worked with...

AndyF::

Sometimes the weird stuff doesn't work. I've built plenty of weird stuff over the years that didn't work so I'm familiar with the drill.

[Tobbemek]

Like i stated before in post#10.  Edelbrock air gap dual quad, with custom adapters for bk/bj carbs.
The adapters to make the Holleys fit  that air gap intake can screw up fuel distribution as well. Making calibration even harder to understand and far from normal procedure.
 On the discussion Holleys vs Carters or Quadrajets by the way, they are all carburetors working and depending on the same physical laws, cfm is still cfm. Yes they have different types of boosters and power enrichment provisions and so on, one just have to understand how to work them properly to get the best out of them. The Holleys have there  "simpleness" ore at least a broader understanding among the Hot Rod and race crowd, other than that its still the cfm vs pump losses we all try to mannish best we can with out fooling ourself with a to big carb.
A little more than 25 years ago i was deeply involved in a NHRA stock legal A/SA -71 HEMI Cuda  that held the European record fore 10 years with the OEM Carter Hemi carbs on it.  Howe fast?? 10.71 pretty impressive at that time, with the "real " old stock rules.
Just saying, a carb is a carb one just have to figure out how it needs to be worked and if it is BIG  enough. 

[Thumperbird]

Thanks everyone.

I think I will try some bigger main jets, 70's, as I feel it is a bit lean at cruise as well as WOT.
When I pull the carbs for the jets I will verify transition slot setup.
I also intend to play with secondary diaphragm springs.
Before modifying the secondary metering plates I think I would drop back to a single carb., I can mount 1 without the spacer, and see how well it behaves that way though I know then i very well might be under-carbed.

By the way, I had adjusted the slip linkage such that the 2nd carb. came in sooner, this seemed to help some of the mid throttle issues I had early on.  I think I will go back to normal setup on this as well, can not be good to crack the second carb. open almost right away and then of course on the top end not fully open.  Maybe the larger mains will satisfy this old issue.

Thanks. 

[Thumperbird]

Had very little to no time to play with carbs all summer.
Current situation is rich idle and cruise, goes way lean after a rich squirt pulse when I get on it at any rpm or gear and still shutters, bogs off the line.  Scoop or no scoop makes little difference in behavior.
No jet changes yet other than going to 32 boosters, lighter secondary springs and have messed with slip linkage timing for 2nd carb.  Lighter secondary springs did nearly nothing, confused by that.
Bringing the second carb sooner makes low end more sluggish.  Have not tried single carb yet.
Overall still fun to drive but just not right at most throttle positions/gears with a pedal stab and likes a slow to moderate throttle push then it picks up at a nice solid and smooth rate.  Smooth as heck in the driveway.