Hey guys. I'm going to try to check my timing for the first time. My car is an '85 Z28 with 305. The CC carb was swapped for a mechanical one, and the distributor in there now has a vacuum connection. Do I need to disconnect any wires from the distributor prior to checking the timing? Since it's a vacuum distributor, do I need to plug the vacuum line INSTEAD of disconnecting wires? My timing light is a basic one with no dial. I do have a tach/dwell meter though. How do I go about checking timing advance? Thanks for any tips! Tim

You do not need to disconnect any wires, but you do need to disconnect and plug the vacuum advance.

After you have the base timing set, you can make sure the mechanical advance is working by reving up the engine while pointing the timing light at the tab. You probably won't be able to tell how far it is advancing, but you will be able to see if it is advancing. What you could do is, with the engine off, set the timing mark on the damper at the 10 degree mark on the tab, then make a chalk mark on the damper at the zero mark. Then move the engine so your new mark is at 10 degrees, then make another mark at zero. Do that one more time, then set your latest mark at 6 degrees and make a final mark at zero. Then, you can start up the engine, and set your timing so at the RPMs where the mechanical is fully advanced, adjust the distributor so your last mark lines up with the zero on the tab. Your base timing will probably be more advanced now, but if you can live with what that does to your starter (if anything), then that would be the best performance setting.

Thanks. I'm going to have to read that a few more times to get it I think Do I want the car to be at 0 degrees or at 6 degrees at idle? Is that with or without the vacuum hose plugged?

What does the 10 degrees mean? Full vacuum advancement?

How do I "move the engine" so the damper lines up? Is it as easy as it sounds?

Sorry for the newb questions.

Whatever the sticker under the hood says, is the stock setting (I honestly forgot what it is, been forever since I've messed with a stock engine). That's at idle, with the vacuum advance unhooked.

What five7 is describing is hand-rotating the engine, little bits at a time, remarking the damper, rotating, marking, until you have a mark that matches what would be the equivalent of 36° advanced. The engine isn't running during this process, so there's no need to worry about any distributor function, advance or otherwise.

Basically shut the engine down, grab the crank pulley (or any other means of rotating the engine small increments at a time), and line up the timing mark that's etched into the damper with the 10° advance mark on the timing tab. While at 10, draw a line that corresponds with 0 on the timing tab. Then hand rotate that chalk line to the 10-spot on the tab, and draw another chalk line at 0. Repeat as five7 says until you've got a chalk line that is equivalent to 36° advance.

A bottle of white out works really well for this, assuming you wipe any grime off your damper first.

Yeah. Grime. I thought I had a piece of roof shingle stuck to my engine. Turns out that was the tab. I hit it with degreaser and it's starting to show some metal. I'll let you guys know how it goes.