Could anyone out there please let me in on adjusting curb idle on a 78 L48 engine with a stock 4BB carb???? I think curb idle is the term the overhauler referred to when telling me that he set it to 500-550?? rpm in drive, engine warmed up. It seems just a bit to low. Perhaps I've been driving Honda's for so long I "can't handle the truth" about Corvette's yet!!!!!!!!!!!!!!!!!!!!!

Photos, adjustment data/specs or references etc would be most appreciated....


mk's78

That does sounds a bit low. I don't have specs in front of me, and maybe someone with a '78 can tell ya, but i would imagine the correct idle speed to be around 650rpm, set with an automatic trans in "D"(with parking brake firmly set!).
Does your car still have the Federal emissions decal on the firewall? That will give the correct idle speed for the car, if it is still there...and readable.
For adjustment info, and other great tips on the Quad carb, check out Zen-Master Ken's Carb Article here.
Click on the link, click on "Ken's Quadrajet". You'll learn more about a Quadrajet than you ever wanted to know!!

J Adams,

Thanks so much for your reply. I did in fact read Ken's Quadrajet article and found it packed with a lot of info for rebuilding etc. However, I am still not exactly sure where? or if there is a picture of the "idle adjustment screw". Is there some way you could point me in the right direction?????


mk's78

Page 4, towards the bottom of the page, if I remember correctly, is a pic of the idle adjustment screw. Turning it in will raise the idle speed, out will lower. Be sure the choke adjustment is correct, and the engine is at operating temp before setting the screw.
Just turn the screw in a little at a time, until your idle speed is up to where the specs are for the car.
hth


                               Adams' Apple2009-02-06 07:42:42

The actual setting is 600 rpm.