Why does my timing change on me?

It seems like I have to reset my timing way too often. Every now and then I park my car to run in somewhere for about 10 minutes, it won't turn over when I come back out. If I let it cool off, it turns over just fine. Nine out of ten times this happens, once I get it started I'll check my timing and sure enough it's 3 or 4 degrees more advanced than where I try to keep it. I'll back it off and it will be fine for a while and then it will happen again.

Does anybody else have this trouble?

This happened when I had a points distributor and it still happens with my Duraspark dist. I have shorty headers but my starter has a heat shield, insulation, and over-sized battery cables.

Thanks everybody, for taking the time to respond!

I'm not sure about the vacuum advance. To check my timing, I unhook the vacuum advance and plug the line. I set my timing at 10-12 deg BTDC. Many times after having the starting problems, I'll check it and it will be 14-16 deg BTDC. My duraspark dist came from an early '80s van. The vacuum advance has two ports, one on top and one on the front. I have the front port hooked to vacuum and the top port is capped. I still have my old points distributor with the single port vac advance. I may try putting it on my duraspark distributor and see how well it works.

Capt Dan said:

Is the distributor turning? Have you marked it to check? If so, maybe your hold down is worn.

Click to expand...

That's a possiblity. I'm sure the clamp is plenty snug, but I've never thought to mark the distributor to see if it's turning under it. If it is turning, it must be vibrating around over time because you can't move it by hand with the clamp tightened down. I have an extra clamp in one of my parts boxes, I'll dig it out and compare them.

By the way, what do the magazines mean when they say total timing? Is that with the vac advance hooked up? The latest issue of Mustang & Fords has an article about performance tips. I think it says ideal total timing is around 34 deg BTDC. My harmonic balancer is only marked up to 30 deg BTDC. Can anybody educate me on this subject?