Ok, I was getting a steady 13" hg at idle and the idle speed screw was in as far as it could go (the tension springs was fully compressed), so something was obviously not correct. I adjusted the idle mixtuire screws out (richer), and the vacuum came down as I did that, so I finally got to 2-3/4 turns out (was at two turns out at 13" of hg) and zero vacuum at idle.

I took it out for a test run and it's definitely better- no more high speed idle when the clutch goes in and the throttle is released, so that's good.

I'm going to try connecting my Autometer tach as use that for tuning and setting the exact idle rpm, but it's pretty close to 800 now.

That's totally screwed up fixes you are going through.

1. MUST FIND ALL THE LEAKS. I have gone through this with my carb 2.2 so I'm no stranger to this issues.

2. Make SURE the carb is not worn out throttle bushing can be barely worn to be a problem or carb is just junk from age and wear. I had gone many stock 5220 holley carbs (few were used and one was "rebuilt assembly style and is no good) and had to go weber due to hard to find rebuilder for particular carb back then, 2004-2005.

3. manifolds warpage at the engine is a usually a problem and have to be checked and the leaks between carb and the manifolds. Ditto to EGR if this one is equipped.

4. Must confirm the ingition timing is set up correctly with the timing gun and the pulley is telling the truth first by checking the cylinder 1 is at true TDC and mark is on the zero degree. And make sure the distributor mechanicals are working freely and sprung.

5. Valves must be set correctly.

Vertify, vertify and vertify!

Cheers, Wizard