How to tell if I have a Vacuum Leak ??

[snomobeelr]

Not sure if I have Vacuum leak. When I pull the big vacuum hose that goes to vacuum booster and breather off the back of the carburator the idle acually picks up, Increases ?? Shouldnt the engine run crappier, not better ?

[Mo's70MCs]

A good start is a vacuum gauge? It depends on how rich it's running, this is probably in idle. What happens when you put it in gear?

[snomobeelr]

I checked the vacuum using the Port on the carb that is hooked to the vacum Advance. I have 7 lbs at idle and 15 to 17 with a load on it. I was thinking I had a vacuum leak when I pulled that back vacuum hose off and the idle came up a bit and sounded better.. I always thought it would run worse if vacuum line not hooked up unless there was a vaccum leak.. Maybe its a wise tale I had heard,,

[Sam (Bones)]

sounds a little rich at idle, but if you only have 7 inches of vacuum at idle, it must have a pretty big cam in it, and may need to be that rich

[Mo's70MCs]

There is a difference in readings...depending on the port. The difference will be whether it's hooked to manifold vacuum or ported vacuum. Manifold vacuum will be constant where ported vacuum will raise and lower depending engine RPM. Reading should be taken with full manifold vacuum. Usually depending on a loppy cam, proper engine operation should result in an even vacuum reading from 15 inches to 20 inches of vacuum with 15 inches of Mercury. Of course there's many other symptoms that will alter an accurate reading.