In Reply to: Re: Vacuum? posted by Bruce (VA) on May 24, 2018 at 21:19:01:
Pretty much the number for most gas engines regardless of configuration. 17-18 Needle steady, Drop to 5-6 on snap accel. 21 on snap decel. Numbers not set in stone, some engines in good shape will run a little lower or higher. I've seen a couple at 21.
I shoot for 17-18 when adjusting the idle mixture and initial idle setting.
Needle movements can be used for diagnosis. Low, Hunting fast,drifting lazily etc.