Thanks yup its stock 292 (except for the 4bbl), but has a big 3" muffler thats about as big as a bathtub on it, maybe thats the "rumble" you hear.
What I meant by the timing maybe wrong is, the DAMPER may have slipped, sometimes they do that. So the MARKS read 12btdc but it could really be 20 AFTER TDC or 30 atdc or just about anything, who knows.
At idle, just try advancing the timing using the marks, go 12btc, 20btc, 30btc, even 40btc. (Make sure to set it back where you had it before you shut it off). If it runs better and the vacuum goes up, thats a hint that the damper slipped or the pointer is wrong or something.
If the marks are "right", the idle speed and vacuum will go up just a little bit until youre at say 15-20btc, then about the same, then at about 30btc or 40btc at idle it will start to skip and run rough. Thats how a normal engine behaves if the damper/marks are right.
Yup Ive had many of these, 194cid, 250cid, 292cid (never had a 230cid yet), all show about 18-19 inches vacuum at idle no matter what carb is on top.
Im kinda wary of the Monojet carb, never had much luck with em. Some folks here like em, kinda like the Quadrajet you just have to be an expert with em I guess. Maybe its just the carb, have you tried a different one?
All my cars are early Novas and came with the old Rochester "B/BC/BV" carb. Not the greatest on gas but very simple and reliable. Find one of those, or a Carter YF, or a Holley 1940 carb, after all you need a spare carb anyway!
