throttle hesitation

[Jac Mac]

I think you will find your problem is the power valve, its a bit lean for your particular engine combination- this is one part in a carb that should be checked/changed to suit each individual engine combo- in this case being lean means you have to go up on the number to cure it- lets say you have a 6.5 now ( ie starts to open @ 6.5" vac ) , try a 7.5 so that it opens a little bit sooner. Holleys were jetted about 5% rich in the 'good old' days to cover most situations, now things are a bit different in this PC world & if 'you' happen to have a good combo with strong vac signal it will hold the PV shut longer & cause a lean condition. This can be real pain in cruise mode & you find yourself constantly having to slow down /speed up to avoid the stumble.

Jac Mac

[BDR427R]

Jay,
I have the same issue with #501 w/ the 427R. My carb has the green dot on it but it is not a slight hesitation but a definate jump. I have never said anything about it because I thought is was the nature of the beast. Should I contact my BDR dealer or notify Roush? The car and motor is just shy of a year old. 1400 Miles. It also appears to leak fuel down the outside of the carb only at start-ups.
Regards,

[jhv48]

This same problem has been documented and discussed many times.

Basically, if you have that stumble, you will probably not be happy until you get a mechanical secondary carb.

For a variety of reasons, the vacuum secondaries don't like these light cars.

Some people have gotten them to work, others just replaced them.

Sounds like you have already spent the time and money to make it work.

Might be time to replace it!

[wtm442]

Originally Posted by Jac Mac

I think you will find your problem is the power valve, its a bit lean for your particular engine combination- this is one part in a carb that should be checked/changed to suit each individual engine combo- in this case being lean means you have to go up on the number to cure it- lets say you have a 6.5 now ( ie starts to open @ 6.5" vac ) , try a 7.5 so that it opens a little bit sooner. Holleys were jetted about 5% rich in the 'good old' days to cover most situations, now things are a bit different in this PC world & if 'you' happen to have a good combo with strong vac signal it will hold the PV shut longer & cause a lean condition. This can be real pain in cruise mode & you find yourself constantly having to slow down /speed up to avoid the stumble.

Jac Mac

Jac Mac - sorry to disagree with you, but the difference of gas getting to any engine with a 65 vs a 75 power valve is very small amount.

The numbers after the dash only determine at what level of manifold vacuum opens the power valve, and never has been an indication of the fuel flow amount.

There are two different "single stage" power valves.

The most common is the standard flow, and a 6.5 "Hg opening is part number 125-65

They also have a high flow unit and and a 6.5 "Hg opening is part number 125-165

If you switched from a 125-65 to a 125-165, then the power valve would open at the same vacuum level, but more flow would go thru the power enrichment circuit.

Before anyone changes the power valve open point (65, 75, 85, 105 etc) you MUST get a handle on the amount of vacuum at an idle, especially with a rude cam! And the vacuum gauge cannot be a cheap one that includes a ton of internal damping. With a cam with a lot of overlap, the vacuum could be going from 15 to 10 "Hg (for example). But a cheap gauge with a lot of damping would stay steady at 12.5"Hg. Therefore, you could install a power valve (10.5) that opens and closes at idle! Been there ... done that. I have a 4 inch diameter vacuum gauge that will follow the vac level of really wild cams.

Holley also builds a 2 stage power valve, but I'd avoid those.

To anyone having tuning problems on their Holley, go out and buy Dave Emanuel's book "Super Tuning and Modifying Holley Carburetors". After reading the book, start over and read it again.

http://www.holley.com/36-136.asp

http://www.buy.com/retail/product.as...01&dcaid=17902

[ekrupa2]

Doug - yes I did receive your email. I will update you as soon as I hear back of the proposed resolution.

Warren - my stumble only occurs during light throttle situations so I was thinking the same thing - accelerator pump.