holley off idle bog

[sweatybetty]

holley 780 on a 440 h.p. engine idles great, runs fine at cruise but has a horrible bog/flat spot just off idle.
i have tried adjusting the idle mixture, advancing/retarding the timing and opening the secondaries a tad bit. nothing helps. this is on a new rebuild kit. any ideas?

 

[demon seed]

What kind of carb, DP'r or vacuum, size of power valve and squirters, intake manifold, cam, and what's the timing set at now, initial, all in RPM and total without vacuum. Ya gotto give us some more information.

Terry

 

[KP]

I had the same type of problem with a 650 Holley and had to jet it down to correct the issue.

 

[cudavert]

In my experience, bogging tends to = lean condition. I'd say primary jetting or power valve opening too late (low vacuum setting).

 

[furz4]

Does this have a stock cam or something larger and what is your initial timing set at. If you have a larger cam in it you may need to add or enlarge the hole in the primary throttle blades to allow more air in and keep the throttle blades on the transition slots at idle. What jets and powervalves are in the carb now?

 

[340sixpack]

Larger squirter?

Welcome back,its been awhile:cheers:

Whats your project?

 

[clifftt]

Did you run this carb before the rebuild, or is this new on your engine? If I recall, that has vacuum secondaries. There are an assortment of vacuum diaphragm springs available (color-coded) which dictate when the secondaries open up, maybe its not opening soon enough (spring too heavy)?

 

[wish4hemi]

There are a hundred million threads on this already. Seems like this same thread gets started every day. Do a search and see what you come up with. I had that problem on my Demon and it turned out to be idle mixture screws and timing (too little initial).