Setting Vacuum Advance with TCS (1972) & Other Issues -----

[Terry M.]

Re: Setting Vacuum Advance with TCS (1972) & Other Issues -----

Bill,
The procedure for adjusting the idle speed and timing for your Corvette is right on the emissions label.

If for some reason that is not legible, the same procedure is in the FSM (Factory Service Manual), but there you will have to sort through ALL the other 1972 Chevrolet line-up. The original emissions label is exactly for your Corvette. If it is a reproduction, one can only hope those folks reproducing the label did so exactly.

If you are attempting to PV the car I respectfully suggest you get the 1968-1972 NCRS Operations and PV Manual. It will tell you exactly how the car is to perform and in most cases exactly how the tester will ask you to operate the car. Get a friend and run through the book several times. In order to pass a PV one has to check and double check the operation of EVERYTHING on the car.

[Jim T.]

Re: Setting Vacuum Advance with TCS (1972) & Other Issues -----

Bill the label Terry mentions should say ignition timing is set with the vacuum disconnected from the vacuum advance unit and the line plugged.
Do you still have the distributor shaft you removed? The top piece is brazed to the shaft and can be removed and installed on your new installed shaft. When the distributor shaft is replaced this is generally the accepted method to keep the centrifical advance the same as it left the factory. From what I understand it has to be positioned on the new shaft exactly like it was when removed from the original one. Years ago the exact shaft was available from GM for your Corvette. In the older GM Corvette parts books there are many listings of distributor shafts for Corvette engines.

[Patrick H.]

Re: Setting Vacuum Advance with TCS (1972) & Other Issues -----

Patrick,

Should it be connected to a manifold or ported source?

When I timed the car, it was done with no vacuum source to the advance unit. Is this correct?

I would really like to figure this stuff out without taking the distributor out of the car - PIA to get back in.
having said that - I have never set the curve on a distributor before.
Might just be better to send it out and have it done correctly.

How long would you think the job would take?

Bill,

For your PV it should be conntected wherever the factory intended it - which I suspect is ported. Checking base timing without the vacuum connected is correct, but be sure you plug the vacuum line to the carb (golf tee works great).

Having the distributor done usually doesn't take long, and if you tell Bill Clupper you need it back soon I suspect you will get it back right away.

To remove the autocam and braze it to the top of your new shaft - most people will tell you that you can never be sure it's going on exactly in the same position it came off your old shaft (if that makes a difference - and I don't know the answer). As a result most people don't do this though I suspect it's possible.

Patrick