My rebuild is reading around 12 to 13 inches vac (at booster hose) and twitches slightly around there. No big sweeps, maybe 1/2" either way. On quick accel, drops to near zero the back to about 18", then settles back around 12-1/2". Cam is Erson TQ40H with 284/296 adv dur., 220/228 at .050, 108 lobe sep. w/ 74 deg overlap and .504 lift on both intake and exhaust. I'm at 5000 ft. elev. Is the twitch a function of the cam overlap? or do I have other issues? Is the low vac a function of elevation? Initial timing is ~15 BTDC, points and plugs, both new, and engine sounds good, but I read the twitch could be valve issues. I bought used big valve C heads, and had the springs checked seated-118#, open-240# w/new keepers, but no other valve work. Comp Cams roller rockers are a little noisy, but doesn't sound like it's coming apart. Thanks for any input.

 

http://www.secondchancegarage.com/public/186.cfm

Good info here.

 

Thanks Trip, or should I say Alex (DeLarge). I saw that site, and it is good info. My gauge looks just like scenario 3 but a couple of inches lower. Altitude? or Attitude???