I just checked the timing on my car with these results. First I idled it at 700 rpm and the initial read 10 degrees on the marker. I then adjusted my timing light to bring the marker to zero. From the timing light I read 15 degrees. I then ran it upto 3500 where max change read 35. I subtracted 35 from 15 and figured mech advance was 20. If I add that to the 10 initial I get 30 total. If I hook up the vacumm right off the intake it pulls to 55 degrees as read from the light. Does this sound ok? My car has a zz3 with a hot cam kit, Thorley Tri Y's and 750 d/p. Rear wheel HP is 275. Goal is 300.

I don't think your motor would like more than 52 total w/ initial+vacuum+mechanical. Set it up to 36 total all in w/out vacuum advance, then if it exceeds 52 with the vacuum advance, add a vacuum advance limiter.

i think your car would really like a crane adjustable vaccum advance can.i am dialing one in as we speak.try 16 degrees initial with the cam style stop at the 2nd to loosest setting.crank the adjustment screw in 8 full turns to start,and set for no pinging + 2 turns(clockwise limits vac advance)aso check threads on "timing" here.
you should check into a mechanical spring replacement kit.usually the medium set(or very near to it)will give you "all in"by 2800-3000 rpm.these springs can be changed one at a time to further dial in your advance curve.a degreed harmonic balancer,timing tape or dial back timing light is necessary to find total advance as well as "all in" mechanical advance.
you will want 34 degrees total advance(with vaccum advance disconnected and plugged),and 12-18 degrees static(no rattle-2degrees at full throttle)set this as close as you can ,then hook up the vaccum advance and go find a hill and lug the engine(not too hard)up it.turn the allen screw 2 turns(clockwise)at a time til the rattle goes away.add two turns and you should be in there.this all depends on your carb,valves and ignition being as well set up as they can be,but it should help.
good luck!
Eric

Originally posted by Mister G:
I just checked the timing on my car with these results. First I idled it at 700 rpm and the initial read 10 degrees on the marker. I then adjusted my timing light to bring the marker to zero. From the timing light I read 15 degrees. I then ran it upto 3500 where max change read 35. I subtracted 35 from 15 and figured mech advance was 20. If I add that to the 10 initial I get 30 total. If I hook up the vacumm right off the intake it pulls to 55 degrees as read from the light. Does this sound ok? My car has a zz3 with a hot cam kit, Thorley Tri Y's and 750 d/p. Rear wheel HP is 275. Goal is 300. It read 10° btdc on the timing tab but the dialback light zeroed it at 15°? What happened to the other 5°? Are you sure your timing marks are true? How confident are you in your dialback light? I would first assure that my timing marks are right on the money with a positive stop, then scribe a 36° mark on the balancer for a reference point. 36° is 10% of the circumference, easy to calculate and mark.

I am not sure why there is a difference. The timing light is brand new (Sears $69). Of course that is no guarantee. The timing should be pretty close. I did set everything up when I put in the hot cam, but again no guarantees there either. I am thinking that the timing light might be giving me bad readings, Perhaps it doesn't work well on an HEI system. Perhaps I should try another timing light just to remove that variable.