Need some distributor help

LVGoat

LVGoat

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'66 389 with 72k miles, un-rebuilt motor, original distributor, still with traditional points. After a hard run through the gears one day it started idling and stumbling, enough so that I suspected maybe a mechanical issue. However compression test and valve train operation are normal, filter element is free of any suspect debris. Car has metal timing gears and a OEM-spec replacement timing chain, which I measured to have 10-12 degree crank rotation before the distributor moves. This seems to be one issue. I plan on upgrading the timing chain to something more robust. Is it possible it suddenly stretched and maybe also skipped a tooth on one hard run?

But then I have this mystery with the distributor. Rotor, cap, plugs, wires, internals all visually look fine, and resistance of all plugs and wires checks out. I checked the dwell, as a then want to check timing. The dwell measured 10 degrees. I had set it to the 31-34 degree spec about 1,000 miles ago. (I thought as points wear dwell should increase?) As I try to adjust the dwell to the spec, the engine bogs and quits at about 15 degrees. Something seems quite off with the distributor. Could a hard run cause this? I did not get to check timing given I can't set the dwell.

Appreciate any help thanks!
 
LVGoat said:
'66 389 with 72k miles, un-rebuilt motor, original distributor, still with traditional points. After a hard run through the gears one day it started idling and stumbling, enough so that I suspected maybe a mechanical issue. However compression test and valve train operation are normal, filter element is free of any suspect debris. Car has metal timing gears and a OEM-spec replacement timing chain, which I measured to have 10-12 degree crank rotation before the distributor moves. This seems to be one issue. I plan on upgrading the timing chain to something more robust. Is it possible it suddenly stretched and maybe also skipped a tooth on one hard run?

But then I have this mystery with the distributor. Rotor, cap, plugs, wires, internals all visually look fine, and resistance of all plugs and wires checks out. I checked the dwell, as a then want to check timing. The dwell measured 10 degrees. I had set it to the 31-34 degree spec about 1,000 miles ago. (I thought as points wear dwell should increase?) As I try to adjust the dwell to the spec, the engine bogs and quits at about 15 degrees. Something seems quite off with the distributor. Could a hard run cause this? I did not get to check timing given I can't set the dwell.

Appreciate any help thanks!
Click to expand...
Do you have another car that you can test the dwell meter on?
I assume the meter has a calibrate function, did you use it?
Are the internal batteries fresh?
 
melsg5... thanks. I don't think it has a calibration, but I have a second dwell meter so will verify dwell that way. Maybe dwell is fine and this is a red herring throwing me off the trail. I'm going through the carbs again (recently rebuilt) as maybe some dirt got in there? Do you think the timing chain slack could be the primary factor?
 
LVGoat said:
melsg5... thanks. I don't think it has a calibration, but I have a second dwell meter so will verify dwell that way. Maybe dwell is fine and this is a red herring throwing me off the trail. I'm going through the carbs again (recently rebuilt) as maybe some dirt got in there? Do you think the timing chain slack could be the primary factor?
Click to expand...
Typically they have multiple scales for 4, 6 and 8 cylinder. Are you looking at the 8 cylinder scale? Are the batteries good.
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Yes, I'm looking at the 8 cylinder scale. Unit doesn't require batteries.
 
Good news is I paused distributor investigation to go over the center carb again. While it was a rebuilt tri-power set-up, I found the choke pull-off had failed. I replaced that and my issues are 85% resolved. But I still have some stumbling, not at idle, but at low throttle like starting off in first. And it almost stalled once going up a hill at modest throttle in second. So now I'm going back to things like timing, dwell, mixture screw settings, etc. I do know my secondary carb throttle plates to not seal perfectly, which I suspect will have some effect?
 
Update: Indeed I had a wonky dwell meter. Dwell seems OK. But I keep finding issues with my rebuilt tri-power. The pull-off had failed and also the center carb accelerator pump was weak. Both replaced and solved my idling and stumbling issues. But now get this... while running well, hot starting was miserable. I found the choke furnace was working BCKWARD and pushing the choke closed when hot versus pulling it open! Flipping the spring inside does not fix it. Perhaps it is a stove for some other carb? Anyway a new one is on the way.
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Thanks for the update. That's strange with the spring.
 
To close this one out, I had three issues causing stumbling, hesitation and hot starting issues, and all related to the tri-power. It was a rebuilt unit and I assumed its parts were all tested or replaced. But the choke pull-off failed, the accel pump was failing, and the last thing I found was a defective, failed or incorrect choke stove that was actually working to close the choke when hot versus pulling it open. New correct stove looks different inside from the removed one, so suspect it was an incorrect part on the rebuilt tri-power. Everything is running great now!

My distributor function is fine (my tach-dwell meter was bad), and the stretchy timing chain (which I'm replacing) was not a cause.
 
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