Steve, I'm having the same problem on my 292. I put a new intake with a Rochester 2bbl and now I've got too much vacuum for the advance. If you've got a port that's above the throttle valves on your carb that should be a ported vacuum. At idle, it's supposed to have less vacuum than say, intake vacuum, so it doesn't screw with your advance. On my carb, it seems to have as much vacuum as the intake ports. I've been wanting to switch over to HEI so, I'm gonna do the swap and put on an adjustable vacuum advance and hope this solves the problem. Probably the first thing to check is where you're connected vacuum wise - determining if you've got a ported vacuum source. Hopefully this your problem and will be an easy fix. And if you get your timing squared away you may have to play with your idle and mixture again to dial it all in.
