Timing is still a mistery for me, stock componants are easy, but this is my first mild hi.po. build. 355 2.02 GMPP heads w/64cc combustion chambers, 282 cam, accel dist.,coil, wires and plugs, now in unplug my vac. advance set my timing and 10 degrees, plug my vac. advance back in and nothing happens, until i give it a quick rev. then it idles up to about 14 degrees, does that sound right? the only reason i question it is because my car will over heat and wont cool off. which i heard is due to too much timing advance. also, i get crazy back fire through my carb under medium to heavy throttle. lol. so i thought it was advanceing too quickly, at which point i went to heavier mech. adv. springs. help me out guys. this build has taken me three years, the car went from toatled, to complete overhaul, i want to drive it damn it! how do i tune the vaccuum horn also?

 

You need to set it for total mechanical advance (vacuum advance unplugged, RPMs up so it isn't advancing anymore). Go for 36 degrees BTDC as a starting point. Most of the time you can just let the idle advance be where it wants to be. With that much cam, you aren't likely to have too much idle advance.

Sounds like the vacuum advance is hooked up to the timed or ported vacuum port. Doesn't get any vacuum from the engine until the throttle is opened a bit. You'd probably be better off with full manifold vacuum.

Running hot and backfire through the carb are more like insufficient timing than too much. You just made it worse by reducing the advance rate.

Not sure what a "vacuum horn" is.

 

The vacuum advance on the distributor, where the vacuum line comes off, i've heard you can tune that with an allen wrench, i thats what i've been told is a vacuum horn.lol.the back firing and running hot w/ insufficient timing makes sense back i did advace it w/o a timing light, just by listening to it and i made it alot better, but i thought it was wrong because my car was running so hot, so i quickly changed it back.

 

not enough advance will get your headers or exhaust manifolds real hot real fast. Everything five7kid told you is correct.

 

thanks guys i took it out and advanced until it pulled all the way through the rpms, it runs great now!