SBC HEI Timing

After paint and detailing my '81 350 engine I recently installed a ACCEL HEI Blueprint distributor that had been sitting on the shelf for a few years. Engine warm and juggling between timing and carb adjustments (Holley 600 w/ renew kit) I adjusted 8 BTDC initial timing w/ vac plugged and had a smooth idle at 700 rpm (manual trans). Reconnecting dist. vac to carb ported vac it had smooth idle and about 30 w/ advance at revs., so pleased w/ that I locked the dist. down, shut it off w/ no run on. I let it cool for 30 minutes or so to see how it would restart. At idle the timing was now at 30*. I quit for the night.

The next day starting the engine cold and after warm up the timing at idle was back to 8. OK, so let it cool 30 min. then restart, timing at idle is now 30. Pulled the cap to see if the mech advance had stuck, it snapped back OK. Tested the vac adv can w/ mighty-vac, it's OK. While I was in there I replaced the ACCEL center plate, weights and springs w/ factory HEI stuff (cleaned and polished the weights and pins) and used Moroso medium springs. Start the engine cold, timing at 8, about 22 at revs which I'd expect for lighter adv weights and heavier springs. Shut off, restart after 40 mins, timing at idle now 22... WTF. Repeat the same process the next day starting cold = 8, shut off, restart warm= 22*.

I installed this dist new when the engine was rebuilt, ran fine for almost 10K when the ignition started breaking up. The coil, module etc tested OK but while it was out I replaced it w/ a points distributor and it ran fine. I found a bad primary wire connection from the PO during the swap so figured that caused the ignition break up.

20K miles on rebuilt engine, 20K on Holley 600 but w/ dip and renew kit from sitting for a few years, manifold vac at carb base is 20 ins. at idle, carb ported vac is 0 ins at 700 rpm idle, vac adv can in dist tested w/ mighty-vac ok, adv weights and springs snap back ok.

My next thought is to pull and clean the distributor (it only has 10K on it tho) but It acts exactly like the mechanical advance is sticking, but am I missing something here?

sorry for the italics, i dunno where they came from

There isn't some sort of delay valve in the vacuum line? Is the plumbing stock, or factory? If you restart it at the advanced setting, does the timing stay advanced with the vacuum line off? Have you got the typical 4 pin module, or is it an Electronic Spark Timing module, which has 7 or so pins? When it cools, does it always go back to 8* without you adjusting anything?

In reply to Streetwiseguy:

The ACCEL dist. came w/ an adjustable vac can but I replaced it w/ a factory HEI vac can while troubleshooting it the first time years ago. No delay valves in the vac line from carb to dist vac can. It also came w/ an ACCEL pickup and 4-pin module, performance center plate, heavier weights and springs. ACCEL cap and rotor are like new. ACCEL Super Coil in cap. The dist body is a factory core.

On a warm restart the timing will stay advanced w/ the vacuum off and plugged.

On a cold start it will return to 8* if I haven't moved the dist. previously.

Not sure what you mean by stock plumbing but no smog or EGR. Rebuilt engine has flat top pistons, 9:1 CR, Comp Cam 260H cam, Performer intake, manual choke Holley 600 and headers w/ duals.

Formatting note: the italics come from using an asterisk for a degree symbol. The forum software reads the first asterisk as beginning the italicization, and the second as closing it.

I'm just here to eavesdrop and learn something. Back to lurking now.

Lock the weights down and see what happens. With the vac disconnected, the weights are the only other thing that can advance the timing. Not sure what heads you have, but I'd look for 36-38 degrees total.

If there isn't a mechanical issue with the advance hanging up, the two remaining issues are the module has some weird stuff going on, or your timing light is broken.