BangScreech4-4-2

Hey, all.

For some time I've been fiddling around trying to get a proper timing curve in my '69 400G. Now I've heard from a couple of sources, (my mechanic who works on my newer vehicles, as well as an article posted here on CO) that there's no need to mess around with a timing light, all you need to do is adjust the distributor for maximum vacuum reading, more or less the same way you adjust idle mixture. Easy-peasey.

It seems a little TOO easy-peasey to me. Opinions?

oldcutlass

It does work on relatively stock engines and will normally get you in the ball park. I use it on old cars where the timing mark is on the flywheel and can't be read. Disconnect and plug vacuum advance. Set your idle speed as low as you can get it and still have a smooth idle. Advance timing until you get the highest vacuum on the gauge while readjusting idle speed back down to maintain minimum rpm's. Once you get the highest vacuum retard the timing until the vacuum gauge reads 2" less than the highest vacuum reading and tighten the distributor lock down bolt. Then adjust the a/f mixture screws on the carb for the highest vacuum and readjust idle for your normal idle speed.

Personally it is not a widely acceptable method and if it were the auto manufacturers would have it in the CSM or tuneup specs. It's a lot more accurate to use a timing light and always repeatable.

BangScreech4-4-2

Still, that's a good synopsis you gave, so I may give it a shot. Couldn't hurt to try. Thanks.

oldcutlass

If you experiment, see what it ends up being with a timing light.

BangScreech4-4-2

That's what I plan to do -- set it using the vacuum method and see what it shows with the light.

Olds64

That's a cool trick. I never heard of it before.