thanks for the relpies, I will update later after I try these suggestions

Hi Listers

I checked the float level - ok, still can't get the idle mixture screws to respond. I guess the next item to go after is another carb to see if that s the problem.

It has the stock 327/350 cam, engine is all stock...

I am cosidering going with a holley spradbore or maybe an Edelbrock afb style carb (I have an edelbrock torker intake, but was trying to make the motor stock looking//

Any other suggestions or ideas ??

Hi Again --

one other question is what is the correct gasket setup for the 68 - I have a gasket, then a thin metal plate and another gasket is this correct ?? this is the setuop I got from the corvette shop , the 68 has an exhaust crossover needing the metal plate ???

Thanks for the help

if your idle mix does nothing... carb needs a rebuild..

As I stated in an earlier post, if your throttle blades are open to far then the idle screw will have no affect. What that means is the engine is able to draw fuel and air from another resource to keep it running. I would review my suggestion about taking the carb off and checking the throttle blade position and adjusting it until it is correct and then try it again. There may be some obstruction not letting the throttle blades close all the way. If they are into the main circuits and can be turned down then that is a 100% indicator that you have a vacuum leak or some other problem that is requiring those throttle blades to be opened in the position that you had them to make that engine idle properly. If they are correct then yes there is another problem with the carb.

What you should do is build a check list of things that everyone has suggested and do them one at at a time and note any change. DO NOT do them all at once or you will not know what change did what.

Its real easy just to jump in and make a lot of changes at once, but reality is you need to do one change at a time. Especially when it comes to setting up and tuning a carburetor.

Rebuild or new carb would be the last resort.

When you are checking all this and setting your timing, do you have the engine up to operating temp?

I had a similar issue (with a brand new Edelbrock carb) -- fuel "dripping" into the carb at idle. Turned out it was too much fuel pressure. Edelbrock carbs work best with fuel pressure at 5.5 psi or less. I added a pressure regulator, adjusted the flow to around 5.0 psi and the problem disappeared. My $0.02 worth. Hope this helps.

I was a tune up whore for 15 years. If your at idle and fuel is driping out from above the float is heavy or set too high. If the vacuum is jumping real fast up and down a few inchs it could be a leaking valve. Most likely a intake valve............................... hope I helped seeya 81zoomzoom

Hi Listers:

I have finally solved the timing advance problem -- I had the timing set to 4 degrees retarded rather than 4 degrees advanced -- duh!!!! after I reset the timing correctly I was able to back off the idle speed screw and letting the throttle plates close at idle, allowing the idle circuit to work and also dropping the vacuum advance port, allowing the engine to return to idle after acceleration.

thanks to all who responded to my postings, this is a great source of knowledge.

well then aftershark had it right

...

congrats on finding problem