Calling all Holley guys!

[msbaugh]

If you can, help me diagnose some carburetor issues I'm having without messing with the air bleeds. 70 challenger, 440, 727, 4000 rpm flash stall, 3.93 gears, 750 Holley 4150 hp double pumper carb mechanical secondaries. Timing is all in at 2500 at 35. No vacuum leaks, floats are set good, and fuel pressure is good at 7psi. Probably forgot something there.

I have been having WOT surging issues almost like detonation. The carb came stock with 73 jets all around, 6.5 PV on both sides. I welded in some O2 bungs to help me and have a wideband digital gauge I watch while testing. Cruise and idle is good but whenever I get into it my A/F jumps up to 15:1 - 17:1 and I get sputtering.

My initial thought was I have low vacuum at idle so I put 5.5 power valves on each side and jetted up on the secondary jets consecutively and tested after each change. I went in increments of 2 all the way up to size 80 and it never had an effect on the wot lean condition.  Then I thought having the power valve at 6.5 probably was actually a good thing as it would richen the mixture 1/2-1 second after romping it, so I put them back in.

I ordered a **** ton of squirt nozzles both bigger and smaller, and some accelerator pump cams to try different ramps. I figure if I try everything I'll eventually get somewhere. Any obvious tips for me here? I can't get WOT to richen up and these are normally super easy to tune

[HP_Cuda]

Let's start at the beginning:

What vacuum do you get at idle?

What is your carb model number? 4779, 4779-1 though 9? (Look on choke tower)

Sounds like you are running lean - not good at high rpm.

B

[msbaugh]

It's about 8-9 " in drive. It's 4150- 80528 carb

[HP_Cuda]

I would strongly make one change at a time when going through this.

To start you need a 4.5 power valve.

Good info on the carb from Holley:
http://documents.holley.com/199r10016-2rev1.pdf

Here are the stock specs for your carb:

LIST #   CFM   STOCK JETTING      POWER VALVE   TYPE
80528   750   (F)72,(R)84      6.5      4150HP

Last question, what are the jets as they sit now and what kind of squirters you have in there?

B

[msbaugh]

I ended up putting it back to how it came. I missed a number when I gave it to you its a 80528-2. I called holley early today and they said it had 73 jets all around 6.5 PV on both sides, the pink cam (is a gradual lift), and a size 31 squirter on both sides. That's how it sits now

[69Superbee]

couple easy things to check, is fuel pressure still 7psi @ WOT and is your needle & seat letting in enough gas?

[msbaugh]

couple easy things to check, is fuel pressure still 7psi @ WOT and is your needle & seat letting in enough gas?

Not sure what size needle and seat came in it. It does have a 30cc accelerator pump. I have a regulator on the firewall with one outlet which then splits for the dual feed before the carb. I have a gauge screwed into the split that reads 7psi at idle. Sometimes after it gets really hot the gauge drops slowly to 0 but the car still runs I think the gauge just doesn't like Heat. Fuel pressure fluctuates +/- 1 psi pretty rapidly but I thought that was normal for a mechanical fuel pump. Not sure how I can verify psi At WOT without the extra work of plumbing fuel lines near the cab

[734406pk]

Check your fuel pressure when your getting on it. Sounds like it may be a fuel delivery problem to the carb. Jet changes will have no effect in this case. Your AFR gauge is correct, lean condition and actual stumbling confirms an issue. More diagnostics are needed here. Post back your results for more help. Good luck!

[cudabob496]

possible clogged fuel filter
or possible vacuum leak?
messed up vacuum advance?

[msbaugh]

Pretty sure no vacuum leak... I'll check the fuel pump pushrod and filter I have installed. Maybe I'll try an electric pump, just hate wasting money after putting on the mechanical pump only 2 years ago

[jimynick]

You may also want to give more consideration to the heat issue. If the line runs near an exhaust pipe or other heat source, it's possible that vapour lock is an issue when the gas boils in the line and the feed is interrupted momentarily. Replace the pressure gauge and run an extension to it so that it's not getting heat soaked and then try running it up to rpm and see what the fuel pressure does. What size is the line and is it possible there's an obstruction/kink in it or a plugged filter somewhere? It sounds to me like the carb is starving at highway speeds and temp when you hit it and it's entirely possible that there's nothing wrong with the carb- except that it's not getting fed enough fuel. Just my 

[stinger]

I've upped my seats to .110 on my 850 and run a 50 cc pump on the rear. also use jet extensions and 33 squirters. pink/brown cam combo. just to throw out some ideas.

[cudabob496]

https://www.youtube.com/watch?v=UPGLUsW5ZeE

[69Superbee]

is your regulator using a return line? if so maybe back off the regulator a bit to limit fuel return, not sure how high pressure your Mechanical fuel pump will go above 7psi, it really sounds like your fuel bowls are draining under WOT.

[cudabob496]

is your regulator using a return line? if so maybe back off the regulator a bit to limit fuel return, not sure how high pressure your Mechanical fuel pump will go above 7psi, it really sounds like your fuel bowls are draining under WOT.

or, at low vacuum, the power valve is opening sooner than it should.

Can tell if power valve leaking, by closing all 4 idle adjust screws, and if engine does not stall,
power valve is suppose to be leaking.