Technical Holley 450 .. sputtering when I take off from stop.

Posted using the Full Custom H.A.M.B. App!I recently put a 4bbl intake on my 264 nailhead and I used a holley 450 on it...im having an issue when I ease the gas from a stop it will sputter but if I get on the gas a little more it smooths out...any thoughts on whats causing this?

 

It could be one of two things, or a combination of both. Your idle speed to to high and ****erflies are open past the idle and transition circuit on the carburetor base or your accelerator pump and squirter are not working properly. You can turn the idle speed down and adjust your idle air screws to set the correct idle. Use a vacuum gauge while doing this adjustment and adjust the idle air screws to achieve the highes vaccuum possible. Do small adjustments on both screws at the same time and keep adjusting the engine idle down. Holleys work great they just take a little tuning. Let me know if you have questions.

 

If it's not a new carb you could have an accelerator pump issue, with the motor shut off crack the throttle and see how strong the fuel shoots out of the squirter, it should fire out of there.

 

Thanks moonman.. my first thought was accelerator pump..ill try these out.

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Some Holleys, including the 0-9776 450 cfm mechanical secondary carb like yours, use a nylon cam to "shape" the accelerator pump shot. These nylon cams are easily changed and somebody may have "tinkered" with yours if you didn't buy it new.

I've run into this problem and my car had the same symptoms as yours seems to have. Holley offers a kit of 5 or 6 different nylon cams which can be interchanged without removing the carb in most cases. The liver-colored cam solved the problem on my car. Good luck.

 

Sounds like the power valve may need to be looked at and maybe changed.

 

Im using the 4548 ..450..its a used carb and I did a rebuild on it...the jets are matching...when adjusting the eccelerator pump..am I tightening the nut to get more spray or backing it off?

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Neither. You want it to have .015 clearance with the throttle wide open.
Loosen the nut to decrease clearance, tighten to open up the clearance.

 

If you search google for holley accel pump adjustment, they have some good vids on how to do it.

Here you go:
http://forums.holley.com/entry.php?428-How-To-Cure-Carburetor-Stumble

 

Hey thanks man!

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No worries, I am fighting the same issue right now with a 390, so it was already handy...lol