Originally Posted by Scotty Dive
...Engine runs really nice, but at idle the engine rpms go up and down. We were wondering if that was because of the cam, but I started to throw a timing light on it and a vacuum gauge and noticed some odd things. Initially the timing was set at about 12 BTDC but that brought only 7 inches of vacuum. When I adjust the HEI to get highest vacuum (17) the engine settles down and RPMs and vacuum is steady, but I cant even see the timing mark. I have an adjustable timing light and I rolled the dial until I saw the timing mark at the 10 BTDC and the dial on the timing light was at 32. Does this mean that to get the highest vacuum my initial timing is 22 degrees? That seems not right. Bad for the engine? Is that what the cam did???
I was taught to time an engine by highest vacuum. Is this different in the AMC V8s?
Hunting idle sounds like vacuum leak to me.
Are you checking timing with the vacuum hose off the distributor and plugged?
Typically you should warm the vehicle up first, then set the timing either at factory specs or a couple degrees above for added performance, then adjust the carb idle circuit for hightest vacuum pulled at the correct idle RPM (that is if all other carb circuits are tuned correctly and are NOT affecting the idle circuit).