I have a '69 351w in my truck with an autolite 2100 carb and factory point ignition. I went through the carb this weekend and it was running great, better than it has in many years. I drove it into town and all was well, but suddenly it seemed to sound "off", and labored to even idle. It seemed to miss, idled low and poorly, shake excessively and would struggle to accelerate. Previous to this it was smooth and very snappy.

I stopped by a friends shop (very convenient) to see what was going on. After proving that it wasn't fuel/carb related (I was sure it was) I noticed that the ceramic coated headers were starting to glow in the daylight! That's about the time we grabbed the timing light. Sure enough it was way retarded.

I verified that the distributor was tight, I couldn't move it without loosening it. once loosened I turned it until the vacuum advance hit the thermostat housing. There it ran very good and I drove it home without issue.

The question is, what happened? If the timing chain had jumped a cog then it wouldn't run so well once I fixed the ignition timing since the cam timing would be off.

If the distributor gear shear pin broke, wouldn't it continue to slip?

If the distributor gear jumped, wouldn't it keep happening?

I am going to pull the distributor tomorrow and look at the gear (mostly so I can get it rotated so I am not hitting the thermostat housing), and am curious if anyone has any thoughts as to what else I should look for. I want to make sure this doesn't happen again.

 

It's possible the distributor gear pin broke and the gear slipped but caught on a stub of the remaining pin and doesn't just spin freely.

 

I am interested to see what you find.. Let us know!

Good luck

 

My dad's pickup did that. It was an ongoing problem until the oil pump locked up. He was constantly adjusting the timing.

 

I pulled the distributor tonight. I checked the gear on it and it looked perfectly fine, it didn't even seem to have any wear on it, which is surprising because it is likely the original part to the motor, so it is 46 years old.

I also checked the shear pin. It looked fine and because it is hollow, I could clearly see through it and verify that it hadn't spun at all.

The only thing I could think off is possibly the vacuum advance was sticking so it hadn't properly returned all the way and I had set the base timing retarded because the vacuum was holding it partially advanced. it seemed to move a little right away, and then after that returned properly each time. The problem is that I can't remember the last time I timed it, so it has been this way a long time.

I put it back together, but rotated everything a cog so it wouldn't be pushed against the thermostat housing anymore. I ran it till it was warm and it ran strong. I backed it out of the driveway and a quick snap of the throttle spins both 35s effortlessly on gravel, so it seems to be running pretty well. I am not sure what to look at next.

Unfortunately, I don't seem to have any marker on it to find TDC, so I wasn't able to use the timing light to set the timing, I had to set it by ear. I guess I should look into getting that fixed sometime as well.

 

Can you run a socket to the oil pump shaft and rotate it a few times to make sure nothing funky is going on with the oil pump?