Quote:
Originally Posted by AM.MSCL
I have a Holley 750 Double Pumper with Vac 2ndaries on my 400 Pontiac in my 69 Firebird. I have a 4 speed manual trans.
The car starts and idles at 900 rpms just fine when cold.
I get on the highway and drive a few miles at 70 mph which is 3200 rpms for the engine; now the car idles at 1200 rpms. I can park the car with it running and push the throttle lever in the direction that will reduce the rpms back to 900. Prior to pushing the throttle lever I make sure that there is no throttle cable hanging to cause the issue. Goose the throttle and it goes right back to 1200 rpms.
Next part of this craziness if I do not get on the high and just drive around the local streets and never get above 50 mph which is about 2500 rpms the idle will go back to 900.
Holley keeps telling me I have a vacuum leak which I have verified that I do not. I have taken Berryman's Chemtool and sprayed lightly around the intake and carb and no rpm change what so ever.
I honestly think something in the Carb is sticking after it has been around 3000 rpms for a while but can not get any help from Holley to check what.
Does anyone have any clues what is going on?
thanks
Ray
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Obviously I am not there, but my bet is that it's running lean when hot. Now the $64,000 question is, why? How far are the primaries open to set idle? If it's got a pretty good cam in it, then, as has already been suggested, you are probably into the transition function. If I recall correctly, the solution for this is to drill a small hole in (I think?) each primary throttle blade. This allows air to enter the engine without affecting the transition circuits.
Shiny Side Up!
Bill