The Stovebolt Site Forums The Shop Area Engine Shop Timing a 350

My 350/quadrajet/HEI sat for over a year and a half while I did the chassis on my 57. I set the timing mark on 6 degrees BTDC, and eye-balled the rotor position. She fired instantly, and seems to run fine (in the garage). I can't believe I hit the mark the first time, so my question is, what is the correct timing for this engine? Also, the distributor doesn't move under a quick throttle-up. I would expect the vacuum advance to move the distributor body. Is something stuck, or am I expecting too much ??

Russell, The usual settings for the 350 is 4 to 9 deg. before. I'm not sure if I understand the second part, but the outside body of the distributor shouldn't move, the advance moves the inside plate. Anyway you must be close if it went right away good luck.

Your vacuum advance only moves slowly. You will not see it move much just reving the engine. As far as advance settings go with the sad stuff the sell as gas. I like to drive the truck and make changes then. I ended up with an idle setting of 6 deg. BTDC with 17 deg mechanical advance and 22 deg vacuum advance. Gas octane, transmission type, rear end gear ratio and kind of use will change the best settings for your motor. It's not hard it just takes time.

I sorta agree, but on accel, vac advance should move up quite noticeably. Set the base timing around 8 degrees, go from there. Drive it hard, should not ping if an automatic, WILL ping lightly if a stick and lugged down a little. If you have loud exhaust, you wont hear it ping.

Oh yeah, GM HEI always gum up inside, especially after sitting. remove rotor, clean and WD-40 weights, make sure they move and return fully smoothly. Check that plate rotates under vac advance.

howziit guys!

i could be wrong, but isn't vacuum advance supposed to be instantly there, as soon as you plug it into the vacuum port(or after tip-in, if you use the ported vacuum outlet?)

and..shouldn't you LOSE vacuum advance, as you lose engine vacuum, and mechanical advance kicks in?

FYI, you can check if vacuum advance will work, by sucking hard, on the vacuum hose(with the engine on, you will hear the engine speed advance).

you will see the diaphragm's "trombone arm" pull the distributor advance plate.

when the engine is idling, the vacuum advance should be activated.

BTW, on some 6-cylinder engines, the vacuum advance moves the distributor.

on most V8's, vacuum advance moves the inside plate, not the distributor body.

5-7 youv'e got port vacuum and manifold vacuun mixed up. The vacuum advance unit should be hooked to the carb venturi port.

howziit kedso!

nope, i know the difference between the vacuum ports; the ported circuit is located ABOVE the throttle plate.

some people actually run their vacuum advance off the ported outlet...

my truck's previous owner had the distributor connected to the ported vacuum outlet. i switched it back to full vacuum "port"(THIS "port" means outlet, fitting,location,spot,source.)

BTW, kedso, not meaning to pick on you. just wondering, for my own info, how you get 17* mechanical advance. i've seen 20*, heard of 22*.

i myself run 10* vacuum advance, 12* initial, 20* mechanical advance.(still searching for the "right" timing combination, will probably try more lead advance.

Good stuff. I knew I could get all the info I needed from you guys. Thanks till my next crisis.