If I set my timing at 8 degrees like it says to, when I reconnect my vacume advance the timing moves to about 18 to 20 degrees. That seems like a lot. do I have a problem with my vac advance?

Sorry; also the idle moves from 600 to 1000 when I reconnect the vac advance.

You may have a problem with the vacuum solenoid that allows vac. to the advance can. I'd need to check the specs to be sure, but Imma thinkin there should be no vac. on the advance at idle speeds, or until the trans is in high gear...I could be mistaken, tho...

I'm not sure how much, but your timing will change and your idle will increase when reconnecting the vacuum hose. It depends too on what kind of cam and compression the car has. If after doing so and everything else seems okay, then it most likely is. What I usually do after setting the timing and reconnecting the vacuum is to drop the idle below the 1000rpm level to where I feel okay with it.
Good luck and enjoy the drive.

The car did not have the correct tach drive distributor when I got it. I bought a rebuilt one through one of the catalogs, I can't remember which one. But I have wondered if it had the correct vac advance on it since it did not specify a 454. Don't they have differant vac advance units depending on your engine.

Sorry Joel; I forgot to mention I do not have a vacume solenoid. It comes off the carb directly to the distributor.

I also have a 71 LS5.  The vacuum feed comes direct, without a solenoid.  The vacuum advance is supposed to be 12 degrees at full vacuum, so you are right on.  You could hold a timing light on it at idle, then pop the throttle open.  The advance should instantly drop to nearly the original 8 degrees, then climb back as the revs come up.

Larry

Thanks Larry; I'll look at it tonight and see what it does. That initial 8 degree's just seems awfully low to me, but thats what it has on the sticker under the hood and my book says the same thing.

Lonnie, follow the vacuum line from the distributor to the carb to see where on the carb it enters. Also, those tachs are the same for small and big blocks from the "General". I'm planning on getting an HEI tach drive distributor and they fit both engines. Check some of the catalogs applications. A couple of other things to consider: are the springs inside the distributor stock? and are the weights they're attached to stock?
~~Again, good luck

I have changed my springs to allow full centrifical advance at 2500 rpm. I used a kit from mr gasket that has several differant springs so you can expieriment. I have it set right now at 30 degrees of advance at 1000 rpm with the vacume disconnected. It seems to run real well but I'm still not driving it due to the interior refurb thats in progress.