Vacume Problem?

If it ran bad any where you had the timing set it's either the vacuum advance is bad like Chief said or it could be what I mentioned earlier about something mechanically screwed up in the dist. causing the magnetic pickup to go out of adjustment when the vacuum advance pulls on it. I had one do that once but it's been 20+ yrs. ago so I don't remember exactly what was wrong. I just remember when the vacuum advance pulled on the plate it went cockeyed and caused the points to go from .017 clearance to about .030 and when I fixed what was loose it was fine. It was a points type dist but the principal is the same. Do you have another dist. you can try in it? If not you can take the dist. cap off and manually apply vacuum to the vacuum advance and see if the pickup adjustment changes. It should be approx. .008 if I remember right.

The ported vacuum on a 750 Holley is the one on the passenger side of the primary metering block. That's where you should hook up the dist. vacuum.

Like Mopekid said you don't have to run the vacuum advance but it does help on gas mileage and also gives a little part throttle boost in power.

BTW: The adjustment inside the vacuum advance doesn't change how many degrees it will advance. It just changes the sensitivity level. Screwed all the way one direction causes it to come in earlier because it takes less vacuum to pull it in. Screw it all the way the other direction and it won't come in until later in the rpm range but it still advances the same amount no matter where you set it.