[67gtospud]

Originally Posted by PontiacJim1959

You may have posted this, but I may have missed it. Is your vacuum advance hooked to manifold vacuum or a ported source on the carb?

If you have manifold vacuum, it will pull in the vacuum advance as soon as you connect it. So if you have set your Intial at 16 with no vacuum advance, connect the vacuum advance to direct vacuum, you now have 26 degrees Initial (16 + 10 = 26) which is way too much and may be contributing to your fast idle speeds. You should shoot for 20-21-ish Initial with the vacuum connected to manifold vacuum - which means Initial at the balancer with the vacuum advance disconnected should be set at 10-12 degrees. See if that will drop your idle RPM's down any.

Dieseling is from too high an idle RPM which can mean the throttle plates are still to far open and allowing gas to be siphoned out through the idle mixture slots - thus your idle speed isnt dropping.

From other carb issues having high idle, make sure the throttle plates are capable of closing completely. Could be hanging up or hitting a gasket?

Next seems to be the idle bleed tubes may require opening up to allow more air through at idle - this is just a suggestion.

5-6 inches of vacuum sounds like a vacuum leak somewhere - that is extremely low. Power brakes? Brake booster? Brake booster check valve?

Sometimes it is best to make a block off plate for one of the carbs so you can work with one at a time and see if blocking 1 off changes any of your numbers - it could isolate the issue.

Vacuum advance is connected to ported source. The vacuum can doesn't begin coming in until about 12" vacuum so I get no additional advance at idle anyways.

The throttle blades are capable of completely closing. They're currently set that about .020" of the transition slots are showing with the throttle plates closed.

By opening the idle bleed jets/tubes what change would that make to my idle mixture screws? Will opening the jets allow more air or more fuel? Will this increase my base rpm? As I posted my mixture screws are currently 1 turn out from closed.

I've check 3 times now for a vacuum leak. Twice with propane and once with carb cleaner. I'm about ready to build a smoke machine and see what I come up with.

I am running hydroboost brakes so no vacuum lines there. The only vacuum lines I have is 1 to the vacuum advance and 1 on the back of the primary carb down to the pcv valve.

Is it possible my pcv valve isn't operating properly due to not enough vacuum thus creating a large, unmetered leak inside the engine?