Idle

On my 78 I have a Holley 750. When it is cold and I first start it sometimes it idles at 1000 rpm and sometimes at 1500. Is there some kind of adjustment I can make so the idle will be the same at startup.

Carbs with automatic chokes have an adjusting screw intended to allow the cold idle speed to be adjusted . There is a small stepped cam under the choke housing that moves with the choke plate . The difference in your idle speeds suggest that perhaps there is some sort of contamination or dirt that is not allowing the assy to move freely . A good spray with a carb cleaner usually will help to acheive a consistent cold idle adjustment . The cam is meant to drop when you bump the throttle in the morning after it runs for a few seconds to lower the idle speed . Dirt can cause problems as this cam moves by gravity when you move the pedal abruptly . Give it a try and give a shout if it does not work for you !

george

It has an electric choke. I've used the carb spray but that didn't help.

Where did you spray it ??

Just remember guys that carb spray is a cleaner degreaser not a lubricator. WD 40 or some onther light oil spray will work better. save the wave

You are right about the wd40 being a lubricant ,,,, and is exactly what you do not want to use . The assy in question must be free of any type of contamination as it operates by gravity to come off high idle . Lubricants can and do gather grit etc which will cause rather erratic operation . I do alot of fuel system work and have run into this problem repeatedly .

gman

All over.

George the piece that can cause the high idle is located between the carb body and the electric choke housing it self . You can locate it by holding the throttle open by hand and moving the choke plate . There is a linkage rod that connects the choke assy and the cold idle cam together and it will move when you move the choke plate . You must hold the throttle open or it will not move ! The piece is a stepped cam and provides a means to adjust the fast idle speed while the choke is in operation . The rpm you quoted was pretty high and these things donot normally go out of adjustment . I would recommend taking the car to a shop to have it adjusted if do not have any experience with carbs .

geo

Thanks