Quick Stab???
 

After I replaced the intake manifold and carb on my 71 with a 307 smallblock, I can't get rid of stumble when you give it a quick stab of the throttle. If you accelerate at a steady pace it doesn't stumble and feels crisp, stab it and it wants to die! Any ideas? Thanks!

Re: Quick Stab???
 

When my truck did that it was the accelerator pump diaphragm

Re: Quick Stab???
 

Thanks I'll take a look at that? This is a Holley 600!

Re: Quick Stab???
 

Mine was to. Although mine was a 650

Re: Quick Stab???
 

Is there a way to check to see if the accelerator pump is good?

Would a bad vacuum advance cause this problem?

Re: Quick Stab???
 

If you look down the throat of the carb,truck not running, and pull back on the throttle you should see it spray. and yes bad vacum advance could do that also.

Re: Quick Stab???
 

Thank You!

Re: Quick Stab???
 

Did you find the problem?

Re: Quick Stab???
 

Not yet, it is getting a shot of gas! ?

Re: Quick Stab???
 

How many miles are on the engine? Could be a slack timing chain. (let's hope not)

Re: Quick Stab???
 

The holley 600cfm (1850) carbs have a dischrage nozzle (squirter) located inside the choke horn. It's held in by a big phillips head screw. You can remove it and put a largert squirter in there to give you more "pump shot". There will be a number stamped on the squirter. You will have to remove it to see the number. Whatever the number is... always go up or down a minimum of 3 numbers to get any effect from the change.

Larger number... more pump shot. Lower number... less pump shot.

If it has the original discharge nozzle (squirter)... it should be a #31. Try a #34 and see what that gets ya.

Also... what vacuum does the engine pull at idle. If it's an automatic... take the vac reading with the engine in gear with the brake on. That way we can determine what power valve you will need as well.

Gary

Re: Quick Stab???
 

When I got home from work, I took a flashlight and looked closely, it seems that no fuel is coming from that nozzle. In fact, the arm to the accelerator pump barely moves no matter how I adjust it, and I can't really move it manually. Should I replace the diaphragm? Thanks... it's been decades since I worked on carbs!

Re: Quick Stab???
 

Gary

Re: Quick Stab???
 

Well...I guess it's time for a new carb! I was going to order the parts for the accelerator pump, but before I took the carb off, I turned the idle mixture screws all the way in, the truck kept running, so I guess the power valve is shot! That's what you get when you buy a used carb. Instead of messing around and taking the carb on/off, I guess I should just buy a new one! Any suggestions on which one? Thanks for all the help!

Re: Quick Stab???
 

You only need a new power valve. Or you have a wicked vacuum leak from somewhere else. Unless you are looking for a reason to buy a new carb... but a new power valve can be changed in half an hour.

What manifold do you have it mounted on?

Gary

Re: Quick Stab???
 

The reason I thought about getting a new carb was because, it looks like in "addition too" the accelerator pump, the power valve is also bad! The carb 80457s looked brand new when I bought it, but every adjustment was way off!
Do you think I should just rebuild it?

The intake manifold is an Edlebrock Performer.

Thanks!

Re: Quick Stab???
 

cant say i have messed with 600's much but do the have an adjustable cam that can be turned to trigger pump faster when throttle is pushed ? mite even make sure vac advance is hooked to ported vac and not manifold .

Re: Quick Stab???
 

THANKS EVERYONE! I replaced the power valve and accelerator pump diaphragm and now it runs like a big block! LOL. It only took a half hour and sure beats buying a new carb, again thanks for everyone's help!

Re: Quick Stab???
 

That video was very informative. Thanks!

Re: Quick Stab???
 

Way cool dude! Glad you got it sorted out. Got your PM as well!

Good job!

Gary