[Rob B]

If you plug the source to the vac adv theres is nothing to cause the adv to occur outside of the mechanical advance that happens with the increase in RPM'S.
In other words if your timing is jumping all over the place with it plugged, you either have a distributor problem or chain and chairs. If the timing stays the same or just varies a degree or 2 and nothing more, you have issues either with vaccumn (carb or leak somewhere) or the advance module on the distributor.

[70temp455]

I know/knew most of this stuff when I played with my 70 Tempest up intil 4 years ago.
I didn't run Prefectly before, it does have min 165,000 mile on it. The the last day I drove it it ran really funky as I stated before. Could be it jumped a gear or (if it does/did have a Nylon gear) broke the brittle Nylon off. I had an olds 350 once that had a Nylon gear and ran great and smooth, then I was at a stop and when I went to go it had died. It broke all the nylon off the gear siting at a stop and I didn't even know it had died..
I'm going to order and relpace the gears and Chain and at least That will be new and out of the equation. Really wish I could rebuild the engine but I don'thave anywhere to do it. Someone buy me a Garage , , Please !
Andy

[bigborehunter]

worn timing chains hide well under fairly high rpm ranges due to centrifugal force making the chain stay outwards. At lower rpm, the chain can flex in and out more easily and hop a tooth that way. Industrial motors can run a long time with bad chains because its a limited rpm range. Then one day they go when starting up and take out the works.

[Lemans1970]

Originally Posted by 70temp455

I know/knew most of this stuff when I played with my 70 Tempest up intil 4 years ago.
I didn't run Prefectly before, it does have min 165,000 mile on it. The the last day I drove it it ran really funky as I stated before. Could be it jumped a gear or (if it does/did have a Nylon gear) broke the brittle Nylon off. I had an olds 350 once that had a Nylon gear and ran great and smooth, then I was at a stop and when I went to go it had died. It broke all the nylon off the gear siting at a stop and I didn't even know it had died..
I'm going to order and relpace the gears and Chain and at least That will be new and out of the equation. Really wish I could rebuild the engine but I don'thave anywhere to do it. Someone buy me a Garage , , Please !
Andy

I think replacing the timing chain and gear is a good idea whether this is causing your problem or not. My 70 has ~231K miles on it and I just recently replaced the timing chain for the 2nd time after it slipped and the engine stopped running (fortunately didn't slip so much as to bend any valves). First time was after around ~110,000 or so.

You should also be prepared to replace the aluminum timing chain cover. These typically corrode over the years. Mine was replaced with each timing chain job. Actually, the first timing chain was replaced only because the cover began leaking due to corrosion, so everything done at once. GM doesn't make them anymore, but the after market ones are great. Ames, PY and others carry them for around ~$170-180.

[70temp455]

Worn SLAP out ! ! !
Checked first by turning the crank past zero and bringing it back to zero. Then I had my brother watch the rotor as turned the crank . I got to 12 degrees before the rotor moved. Suspision confirmed. Then I torn into it and got the timing cover off (between thunderstorms). There is so much slack in the chain that it could have jumped a tooth.
Anyhow, I'll have the new NAPA chain and gear set in the morning and if it doesn't rain too much, I hope to have it back togeteher tomorrow and hopefully be able to put Fire to it.
Andy
ps The cover looks to be in good shape. It's covered in 1/2" of oil and grime and well preserved (lol)