carb issues

[mustang_gt88]

I have a holley 600 that idles great, but when it driving down the road the carb stumbles. Its fine if i keep the rpms low, and when i dump it kicks hard. Once the car has warmed up it gets betterand the stumble almost gone. any thoughts?:confused:

[MFIELD]

Vac or mech secondaries?

[mustang_gt88]

vac secondaries

[85_SS_302_Coupe]

Does the problem go away at WOT or does it stumble when you go from cruising to accelerating? Might be a bad accelterator pump diaphragm.

[mustang_gt88]

At WOT the car runs great, it stumbles when i go form cruising to accelerating

[85_SS_302_Coupe]

Definitely sounds like accelerator pump issues. There's a little rubber diaphragm in there that looks like a tiny rubber umbrella, they go bad and that causes a symptom like this.

[mustang_gt88]

Thanks, do you know were i can pick one up at?

[85_SS_302_Coupe]

Let me rephrase that...not the diaphram, Holley calls it a check valve, http://www.holley.com/26-41.asp The diaphragm looks like this http://www.holley.com/135-14.asp

Of course it might be the diaphragm too, they're all part of the accelerator pump and can wear out and go bad. The check valve is about $6 from Cincy Speed last i checked. I doubt a parts store would have just that piece, they'd have a rebuild kit that might have it.

If you take the carb off, or just the front bowl off, on the bottom the little square thing that has the arm coming off, that's the accelerator pump. Take out the 4 screws and look inside and see how it looks. When mine did this, i took it apart and the little check valve had broke at the stem and was laying inside the bowl.

[mustang_gt88]

thanks for the help