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I have had to adjust my timing several times over the last several weeks. When first adjusted to approx 7° btdc, it runs great…for about 4-7 days. I have now run out of room to adjust it further. (Meaning I am against the upper limit of the slot). I’m sitting at about 5 btdc and running a little rough, but I’m sure I will soon be at zero (and then worse) and barely running. Any thoughts on what’s going on here?
Did you do any work on the engine before this started? If so, the issue may be related to that work. Also, check that the distributor advance plate and vacuum advance mechanism move freely and smoothly. Old dried up grease may be causing the plate or advance weights to stick.
By any chance did you disassemble and rebuild your distributor? I did, and found that when I inserted the dizzy I couldn't advance it enough (reached the end of the slot), then when I pulled it and reinserted 1 tooth over, I couldn't retard it enough (other end of the slot). :wtf::scratchheadyellow:
Eventually I realized the dizzy drive gear has an odd number of teeth, but the other end of the dizzy shaft has a pair of opposed posts coupling it to the centrifugal advance mechanism, so if you rebuild the dizzy with the advance coupled to those posts the wrong way around, your ignition timing can wind up a "half tooth" off at best no matter how you adjust the advance. Pulled it out and apart again, flipped the advance around on those posts 180°, reinserted and had the proper range of advance adjustment again.
That said, 5° of advance shouldn't cause rough running, just low power and mileage, so you may also have something else going on.
I did not do any work on anything related to this. I definitely didn’t remove the distributor.
I didn’t do any work related to this. About 2 months ago it was running really rough and no power. When I put the timing light on it it was approx 10° atdc. I adjusted to about 7° btdc and it ran great, normal power and great mileage. That lasted about a week as it slowly deteriorated to about tdc. I’ve adjusted timing a few times since and it’s good for 4-5 days. Now I’ve run out of room to adjust any further.
Thanks for the background info. It's always helpful to know what work has or hasn't preceded a problem.
With the timing light connected, gradually rev the engine and see if the timing mark advances. Do it with the vacuum hose connected and disconnected (and plugged). If it doesn't advance or behaves erratically, the distributor likely needs attention. Some penetrating oil on and behind the advance plate may help, but a through disassembly and cleaning seems the best lasting solution.
While you're at it, check that the vacuum advance chamber holds a vacuum and moves the advance plate. Inspect the vacuum line, too. If either leaks, the engine won't run well.
Thanks for this. What I’ve done so far: confirmed advance chamber holds a vacuum and moves the advance plate, put some penetrating oil on and behind the advance plate, and replaced the vacuum hose on vacuum advance. Seems to be running better, but haven’t given it a real test yet. It got dark and I got tired. It’s sitting at about 7-8 btdc and not maxed out on the adjustment slot. I will take a harder look at the distributor when I can (or if my modest improvements don’t hold). Really appreciate your input.