128racecar

Almost done setting up the dual quads on my 1957 283/245 HP. It has been running a 7300 FI for the last 50+ years, and I am converting it back to it's original configuration. Quick question: Is there supposed to be an idle set/stop screw on the driver's side of both the front and rear carbs? I'm not referring to the mixture screws in the middle. There is only one on the rear carb, so I was wondering if I am missing one.

Thanks for the help!
Marc in Indy

Frankie the Fink

If you are running '56 carbs or EARLY '57 carbs they will have idle air bypass screw in the bass - usually brass colored - the only Corvette WCFBs that have these (red arrows)..

128racecar

Okay, I didn't describe it right. I guess I meant the steel colored screw just in front of the pivot point for the butterfly linkage. Maybe a fast idle screw? I can see it on the rear carb in your photo, but the angle hides if there is one on the front carb.

Thanks Frankie!
Marc in Indy

Frankie the Fink

Here are the Corvette early dual quad adjustments...

Frankie the Fink

There is a rear carb idle speed screw, can't remember if there was a front carb adjustment and none of my pictures show it..

L78racer

Some 2x4 front carbs did not have idle speed screws. The curb idle is best set by using the rear carb.

Frankie the Fink

This is the definitive shop manual on the WCFB dual quads....
https://www.google.com/url?sa=t&rct=...U0PFSg&cad=rja

jrm5657

Marc,
The front carb generally does not have the idle screw, your throttle blades should be closed on the front carb and your idle speed should be set with the idle screw on the rear carb.
Hope to see your car this summer some time!! Stay warm.

Jim

Frankie the Fink

BTW - those carb base idle air bleed screws are hard enough to get tweaked most just close them off (turn them completely in) and use the traditional speed/mixture screws.....I did...

128racecar

Thanks, Frankie, L78racer, and Jim!!!

My car has the later carbs without the idle air screws. However, the dual quad section in the manual Frankie lists above is superb at detailing how to tune these carbs. I got the best idle speed/highest vacuum setting with the mixture screws varying between 3/8ths and 5/8ths turns out from fully closed. It is easier to adjust them with a small open end wrench than a regular or 90 degree flat head screwdriver. Only the #4 screw is tough to reach with a wrench, and even it wasn't so bad. As Jim mentions, the rear idle screw is all that is needed to set the idle.

Once the Mrs. helped with setting the linkage correctly (she thinks it's WAY better than bleeding brakes!), it was time for a test run. It was an unseasonably dry 50 degree day here in Indy today, so I hit the jackpot. The dual quads started cold and hot perfectly, idled smoothly, and best of all, it accelerated like Jack the Bear when I nailed it!

Thanks for the help, guys- as always, this forum rocks
Marc in Indy
1957 Corvette 283/245 4 speed, in the family since the early 60's
1972 Corvette 350 base auto loaded

Frankie the Fink

This motorcycle tool is what I used to get on those 1/4" rear mixture screws....with no bit in the drive its 1/4". I've had one laying around for a long time; pitposse.com has them but you don't even want to know the price...if you do you can find it out...