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

[cjshaker]

Drew, are you referring to original BJ/BK carbs, or the repros? While they didn't specify, I think the ones he got from Bob were the repros.

[FElony]

Felony, his measurements are way off. The ifr and emulsion specifically. I don’t think he realized the ifr is inside the idle well.

Well, I trust you more. I mean, he worked on potato chip machines and you roam the high seas in search of Megalodon and the Giant Squid. Easy choice!   

Seriously, I am trying to get re-educated about Holleys to a higher level than I once had. Between all the loose and on-car carbs, I betcha I have at least 100 of them. I monkeyed around a lot in the old days with jets and pump cams and shooters and all, but not too much beyond. I know EFI is the big thing these days, but I'd rather tinker with old tech. 

[Drew Pojedinec]

Drew, are you referring to original BJ/BK carbs, or the repros? While they didn't specify, I think the ones he got from Bob were the repros.

I’m referring to originals which I thought chip mech was as well. Either way a .042 ifr would be crazy.


I’m with ya felony. Tho often frustrating I prefer old tech as well.

[Thumperbird]

Moving accelerator cam from 2 to 1 definitely helped with a low speed launch, less hesitation.
At the same time though I feel like I lost a little bit of power going into second around 4800 RPM's.
Almost like I traded performance from one to the other.
Have not messed with any jets yet, trying to get as far as I can with existing setup and go from there.
Idle is still rough but better after playing with mixture a bit, I noticed that choking the idle air bleed did make idle worse of course, makes me think I should try going the other way on that as previously suggested.  Have not messed with accelerator nozzle size but that is next I think.
Thoughts on this?  Thanks.

[WerbyFord]

@Drew - thanks for posting that detail about the BJ/BK specs. Well said re the high-dollar 600 Holleys. Other than the linkage I've had good luck making dual quads from just about any twins, its just a matter of setting them up. On the secondaries, my 1964 shop manual says the BJ/BK got a #11 plate, which is a secondary hole of .079". Actually a bit richer than the typical 600 Holley. But other BJ/BK sources I've seen show those very lean holes in the secondaries.

I see a lot of "dual quad" calibrations with leaner secondaries (like the carbs Edelbrock sells to go with this intake!). Not sure why there would be such a trend if there is one. I did find that my best jetting for twin AFB's on my FE was a little leaner than the best setting for either of those AFB's when used as a single-4v carb. Hmmm. This was all done using the GTECH, not a fancy O2 meter.

@Thunderbird - We once had the problem you describe on our 4100 autolite powered truck. It would cruise ok, but if you got into it at all, it would start "chugging" like it had about 3 plug wires off. Turns out, the booster assembly had pulled loose in the secondary (yes, they are multi-piece if you look close). Never seen that before. So of course the secondary main system was really screwed up * that's how it ran.

What I always do is try each carb of a dual quad setup first as a SINGLE carb on a good running 4bbl engine. Make sure I'm totally happy with it as a single 4bbl before I put two of them on and then cant tell who is the bad guy. Not sure if you have another (old) car you could try that on with each carb.

[Drew Pojedinec]

Werby brings up a good point. I build about four sets of 2x4 1850’s a month. While testing out often they’ll be off base. I also tune each one on my truck when that happens. Easier to narrow down a minor issue.

Werby, maybe they changed the plate at some point?  On my custom carbs I typically wind up larger on the secondary.

[Thumperbird]

Been playing some more.
Here is where things are at, and what I am planning next, looking for feedback.
Set rev limit on my MSD high, it was choking things off almost a 1000 rpm before set value.
Learned something after this as I had not run it up in the 5000+ range much.
Seems to run lean at wide open throttle but here is what is interesting, I suspect it's the secondaries coming in kind of late but quite frankly never experienced this before.  Running rich and a little choppy still at idle.

It pulls fairly hard from 3000 to say 4500, then seems to soften and maybe even shudder a little, then at just over 5000 rpm's it smoothes out really well, still lean but not as much, and pulls hard to 6000, did not go beyond that.

Thinking of doing the following, want to minimize carb removals as the duals are a pain in the rear.

1.  Main jets are 66, bump to 70
2.  Try some softer springs in the vac. secondary diaphragm, I think the thing is a thirsty pig and starving for fuel at higher rpm's
3.  Squirters were bumped to 32 a while back, going to try 35's
4.  Check on secondary restriction size when carbs are off and go from there, if they are the small flavor will drill them out
5. Double check transition slot and set them up so they are less than square and secondary is more in the game

Thoughts everyone?
Thanks.

[Barry_R]

Do not know if it relates...

On dyno when running vacuum secondaries you will often see them roll rich just before the secondaries open up - probably as air demand approaches the limits of the primary side.  Then as the secondaries open they will have a lean hole as the rear main circuits are activated by airflow.  So you get a few hundred RPM of "upsie-downsie" before things stabilize.  Changing the secondary rate springs until the opening point most closely matches demand cleans this up, but might not be reflective of what it wants "in the car".  You could be moving through that fuss point.

On dyno I will sometimes wire tie the secondaries to open so I can isolate WOT A/F tuning from the opening rate tuning.

The .015 pump setting is at WOT as Joe referenced, but I have also seen those set wrong.  On race only applications I am guilty of doing that - setting them loose - so that the full pump shot is available when leaving off the converter at higher throttle opening positions (like 4000 or so).  Otherwise you have less pump shot left when you go WOT.  On street stuff this approach will not work - you need to set them up as Drew says - no clearance at idle.

[andyf]

With as much money as you have invested in that engine you should have a wide band in the exhaust. If the carbs are off you can ruin a new engine pretty quickly. We see it all the time at the engine shop. Guys pay $10K to have a performance engine built and then they don't tune the carb and before long they are back in the shop with cylinders wiped and valve guides shot.

[WerbyFord]

An easy thing to try:
Lock both secondaries SHUT (easy to do, no need to pull carbs) and see how it behaves a a 4v like 0-2-0-2 barrels.

Then leave each one locked shut but let the other one open (so you have a 6v like 0-2-2-2 or 2-2-0-2 barrels.
Easy to try and you might learn something qualitative.

Agree on the wideband though - I don't tend to run $10,000 plus engines but if I did it seems that would be a small added expense to get all 8 barrels happy.

[Drew Pojedinec]

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.

[Thumperbird]

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.

I wish there was a way to delay the pump shot, have done a few 3000 launches and it goes fine but wonder if some extra fuel early on could compensate for lazy mains or ?

I will play with secondary on/off and spring setup before the main jets and see what happens.

As for the rough idle, what is the collective opinion on setup of primary and secondary in terms of the transition slot, etc.?  From reading, it sounds like on a dual quad, a good starting point is less slot exposed on both carbs than say a single 4V.  I feel like the air bleeds are not quite right in my setup, wondering how much of that I can compensate for with transfer slot and secondary setup?

Also, am I crazy to think that this thing is and will pull hard beyond 6000?  I did do a fair amount of work on the heads and intake runners but nothing too crazy.

Thanks again everyone, I need to get comfortable with spending more time tweaking and testing, just tough to get used to testing at the higher RPM's in a suburban environment.   

[Drew Pojedinec]

I need to borrow a set of these replicas and record the calibration. I understand they
Are different than the original, which I guess doesn’t make them replicas.

[Thumperbird]

Drew,

I would have no problem sending them to you this winter, by then I should have dialed them in better so there would be a reference to a 445 stroker build, would of course document all changes I made.

Driving season is so short where I live that I want to just keep tinkering and taking some joy rides for a while here.

Starting to wonder just how impactful the extra large plenum volume is to carb. behavior.

Thanks. 

[Drew Pojedinec]

Cool. Lemme know, I’d be happy to pay shipping both ways for the knowledge.
I suggested the larger pump shot due to that large plenum. I’ve never messed with that particular intake, but Jays dyno testing showed no major abnormalities.