Retarded timing issue

[jdweaver]

My 140 horse '65 Monza has the most peculiar timing flaw. Timing advances normally till about 1500 and then begins to retard. It retards to the point that at higher RPMs I get back fire thru the carbs. Vacuum is disconnected when I do this timing run and the previous owner insists it is the original distributor (but who would really know on a 50 year old car?).

Weights on the distributor seem to be ok...not hung up or sticky. Anybody got an idea...?

thanks...

[64powerglide]

I'm no means a mechanic but I had a Lincoln that back fired like that & it turned out to be 2 broken valve springs. This was a 460 & only backfired when I got on it hard. You could have a real weak one or a broken one.

[bbodie52]

Welcome to the Corvair Forum!

In 1970, when I was 17 years old, I remember completely disassembling a distributor, carefully cleaning and reassembling it, and reinstalling it in my Monza. There was just one problem... it ran terribly! It started and idled well, but it had no power when I reved the engine. The more the engine's speed increased, the worse it ran!

I put a timing light on it, and the timing was fine... until the engine RPM climbed. I discovered that the timing shown by the timing light was going the wrong way! Reving the engine caused the timing to retard! The vacuum advance knew which way to go, but the centrifugal advance was headed the wrong way!

How could that be???

I discovered that when I put the centrifugal advance weights back in I had flipped them upside down, and had created a centrifugal retard! I didn't know that was possible, but there it was. I took the distributor breaker plate off, removed the centrifugal advance mechanism, and reinstalled it correctly. The engine was happier, and so was I!



If somebody took your distributor apart to clean and inspect it, it might have been reassembled incorrectly. You might have to pull the breaker plate and take a look. When the weights spin they might be sitting on the wrong side of the distributor cam, and when they move outward against the springs they may just be rotating the cam the wrong way.

In the picture below, you can see that as the weights swing outward toward the distributor housing, the portion of each weight that contacts the distributor cam in the center would apply leverage that would rotate the cam clockwise, which would have the effect of advancing the timing. HOWEVER, if the weights were removed, flipped over, and reinstalled so that they were pressing on the other side of the cam base, the weights would rotate the cam base counter-clockwise — RETARDING THE TIMING. This may be the problem you are encountering on your Corvair distributor.

[jdweaver]

That is exactly what it seems like. I've pulled the distributor and will dig into it...little else makes sense. And to Jeff's comment on weak/broken valve springs, that wouldn't effect timing in any way, though it could create some miserable running conditions.

Thanks guys...I know I can always get a fresh perspective when I come here...

Let ya know how it looks this weekend...

[ac1948]

If vacuum is decreased by leaking intake valves the timing will be retarded by vac. advance unit. I had this problem with a 140. With broken spring, the valve would seat at low rpm but bounce as rpms came up. This caused the low vacuum. Jerry