Accelerator Pump Nozzle???

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wazoo64

wazoo64

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I have a new 750 QFT on a 500HP 408 and when it leaves from a stop it hesitates. I was told to increase the accelerator pump nozzle to fix this. I have bumped up from a 31 to a 40 and it is much better.
I am wondering what is typical and if there is any other insight I need to know about these.
 
Nothing really typical. Every combination is different and has different requirements but a 40 is a pretty darn big squirter. If that fixed the problem your fine but if it still has a little hesitation I'd suspect you might be running a little lean. That'll cause a hesitation also. You might try bumping up the jetting one notch.
 
fishy68 said:
Nothing really typical. Every combination is different and has different requirements but a 40 is a pretty darn big squirter. If that fixed the problem your fine but if it still has a little hesitation I'd suspect you might be running a little lean. That'll cause a hesitation also. You might try bumping up the jetting one notch.
Click to expand...


I dont know much about tuning carbs. If you have any advise or good articles to read on bumping up the jetting let me know. Thanks
 
Could be a few things lean idle circuit [which would show it self say driving though a parking lot in 1st slowing and going w/4 spd], wrong power valve rated too low of a vacuum, wrong pump cam[not enough shot duration.
I think you should get a book on holley design carburetors to better assist you.
But if you have an auto trans [maybe with some converter] you will find your self running a larger shooter like you have.
Basically if go's then bogs then too big a shooter, if it hesitates then go's not enough shooter.

On mixture, they used to sell a glass spark plug that you could see the color, anyone here have one? get a good light and magnifying glass and look at the color of the porcelain where it meets the base in side the plug[due to todays clean burning gas]
 
Your best bet is to get a carb. tuning book. You'll learn way more from it than I could post here in an hour. Holley has some good tuning books out. Summit probably sells them. If not Amazon.com should have them. I know you don't have a Holley but your carb is the same design so the Holley book will work.
 
3404spdvaliant said:
Could be a few things lean idle circuit [which would show it self say driving though a parking lot in 1st slowing and going w/4 spd], wrong power valve rated too low of a vacuum, wrong pump cam[not enough shot duration.
I think you should get a book on holley design carburetors to better assist you.
But if you have an auto trans [maybe with some converter] you will find your self running a larger shooter like you have.
Basically if go's then bogs then too big a shooter, if it hesitates then go's not enough shooter.

On mixture, they used to sell a glass spark plug that you could see the color, anyone here have one? get a good light and magnifying glass and look at the color of the porcelain where it meets the base in side the plug[due to todays clean burning gas]
Click to expand...

Lots of info. Thanks. I run an auto trans with 3000 stall. It is definitely hesitating not bogging. The larger shooter has helped I just didnt know if I should going bigger to get it perfect. I am very close.
 
one more thing on the accelerator pump ....make sure there is no slop in the linkage...as soon as the throttle moves the pump shoots gas....

otherwise that can/will cause a bog.
 
fwaugh said:
Lots of info. Thanks. I run an auto trans with 3000 stall. It is definitely hesitating not bogging. The larger shooter has helped I just didnt know if I should going bigger to get it perfect. I am very close.
Click to expand...

Maybe a 42, but you need to change to the corresponding pump cam, otherwise you'll be chasing your tale.lol
 
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