Holley Carb Stumble

[rednine4]

I am experiencing a hesitation/choking out when I floor my BII from a dead stop. I have a stock 302, with a Holley Truck Avenger 470 carb. I have tried the basics from what I've read online and watched on youtube videos, however nothing has worked.

I've adjusted the pump shot which seemed to help reduce the stumble, but not nearly enough.. The truck runs great at all other speeds. I can floor it while moving and it usually just stumbles at first then catches up. If I floor it from a dead stop, it either stalls for struggles. Adjusting the fuel pressure seems to have no effect either.

My guess is that it's getting too much fuel, but I could be wrong. Anyone know where else to look?

 

[Explorin94]

Was this carb new when you put it on? If not how long did it set before you put it on the truck? If it was run and taken off and had sat for a while then I would say that your accelerator pump is bad or the accelerator jets under the choke flap are plugged up.

 

[rednine4]

Brand new out of the box. Maybe sat for 2 weeks. And it's the latest version of the T/A #2 as opposed to #1 which had probs.

 

[superdave1984]

Bump the timing a couple degrees.

 

[SpongeRanger]

Take a look at this thread.

http://coloradok5.com/forums/showthread.php?t=166055

Hope this helps.

 

[rednine4]

tried bumping the timing yesterday and no difference. I think it is low fuel pressure. the carb needs 5-9psi and my gauge reads 6.5. it seems to only choke out when the secondaries come open.... I am going to remove my fuel pressure regulator to see if that helps.. if not I will have to get another fuel pump i'm thinking.

 

[originalnitro]

Your ok with 6.5 psi.
What spring are you using for the vac sec

 

[baddad457]

tried bumping the timing yesterday and no difference. I think it is low fuel pressure. the carb needs 5-9psi and my gauge reads 6.5. it seems to only choke out when the secondaries come open.... I am going to remove my fuel pressure regulator to see if that helps.. if not I will have to get another fuel pump i'm thinking.

Your fuel pressure is fine. Fuel pressure has nothing whatsoever to do with it. This is a carb, not fuel injection. The fuel pressure is only one part of the equation in supplying the fuel to the carb, which only fills the fuel bowls, none of this has anything to do with how the fuel gets from the bowls into the airstream flowing thru the carb throats. And it takes awhile to empty the bowls when they're full of fuel. The motor will run for several miles before that fuel runs out. When you nail the go pedal, the vacuum in the motor is the only thing pulling fuel from the carb, and that falls to zero when you nail the pedal. This is what the accellerator pump is for. The accellerator pump needs to have the slack taken out of the linkage, pure and simple. And as Superdave has intimated, you probably need to bump the timing up more. What is the initial timing set at ? And the secondaries should not open instantly on this carb, it's got vacuum secondaries, not mechanical. Especially if you've never changed the factory sec. spring. If you have not, the secondaries are far from opening at a dead stop stomp. All you need to do is learn more about the workings of a carburetor here.

 

[rednine4]

Yes, some very good points..you were right. I went through and adjusted the pump shot and it works good now.

The only thing is I wish it had more balls.. when I floor it it just hooks and goes but it wont spin the tires. I just figured that a BII with a v8 3.73 gears and C4 i would be tearing ass more...

 

[baddad457]

What size tires are you running ?

 

[baddad457]

You might also try more timing and making sure the vacuum advance is working in the distributor. You want as much timing advance as the fuel you're using will allow and not get pinging on accelleration.

 

[superdave1984]

You may need a looser torque converter. You are losing torque somewhere between the crank and the tires. Either that or your engine just lacks power.

 

[originalnitro]

What did your 302 come out of?

 

[rednine4]

Tires are stock size... I guessing 28"

Timing is set at 12 degrees BTDC

I have the vacc advance hooked up to the dizzy.. how can I test that it's actually working? I would assume it would work OK because it's brand new out the box.. not sure the vac advance would be a culprit at WOT conditions?

T/C is stock Daaco F26

302 is out of a 90 mustang GT... Its mostly stock e7 heads, edlebrock performer intake, Holley T/A 470 carb, Explorer camshaft, AA headers..

I have other cars with 302's and this just doesn't have the snap to it.. might be the combo here or maybe im just being picky

 

[baddad457]

Tires are stock size... I guessing 28"

Timing is set at 12 degrees BTDC

I have the vacc advance hooked up to the dizzy.. how can I test that it's actually working? I would assume it would work OK because it's brand new out the box.. not sure the vac advance would be a culprit at WOT conditions?

T/C is stock Daaco F26

302 is out of a 90 mustang GT... Its mostly stock e7 heads, edlebrock performer intake, Holley T/A 470 carb, Explorer camshaft, AA headers..

I have other cars with 302's and this just doesn't have the snap to it.. might be the combo here or maybe im just being picky

Unplug the vacuum hose from the carb, remove the distributor cap, and while looking down into the distributor, suck on the hose and watch to see if the breaker plate moves when you suck on the hose. With that setup you should have gobs of bottomend torque. I ran basically the same setup in mine when i sold it, with the only exception of a set of 1.7 Cobra rockers and a 570 Street Avenger carb. All I had to do was nail the pedal to roast the tires (3.73 8.8 Trac-loc and 275/60 15 tires) I did have a set of home ported E7's too, with just the exhaust sides opened up. Might also go up to 16* BTDC, it's also possible the balancer outer ring has slipped, throwing the timing off. Getting the #1 piston to TDC(on the firing stroke) and noting the position of the timing marks to the pointer will confirm this. Also what distributor are you using ?