Vacuum advance still far too aggressive after crane adj unit

[crazypete]

I know I posted on this before, but I wanna throw this out to the community before I finally decide to scrap the system and cap it off. I could use that extra 1-2 mpg, even though I'm getting 20 mpg with a carb and 3.73's (I have no idea either!)

I'm using an 85 mustang distributor with a holley 670 street avenger. I get 20 hg's vacuum at idle (1100 rpms, but same happens at 800 rpms), I'm not running egr or air pump and I have no spacers or anything else in the way. Based on how smooth it runs, I do not have a vacuum leak. Running base timing for now : 10 deg. Yes, I am using the spark advance port on the carb =) . Mixture guage shows stoich + 1 bar.

Originally, what was happening is that, with the light aimed at the timing marks, I would connect the vacuum advance at IDLE and see the marks shoot off to somewhere under the motor and it would run like crap and backfire immediatley when I touch the throttle lever by hand. Holley said it misdrilled it's spark ports on some of the avengers and they sent me a tested unit under warranty.

Ok, now, at idle, no problem. I hook it up and see no change. Cool, I think. I reach over and blip the throttle. BANG!! BANG!!! I can feel the backfire go up into the carb. I see the timing marks jump way up to just past 40. Darn it.

Ok, I get the crane cams adjustable cannister and allen wrench it all the way out. Same behaviour. I allen wrench it all the way in. Same behaviour. This is so annoying! What is going on with this silly car?