Re: Stumble (miss) at Idle. Please help.
Frank,
As I read it, you have observed three problems.
1. An intermittent miss, like a dead or weak cylinder.
2. An off-idle stumble
3. A PowerGlide that shifts into Reverse or Drive with an occasional bang.
If I've misunderstood, then just ignore the rest of this posting.
1. The intermittent miss.... the suggestions you've already received about ignition issues make sense. I have nothing to add.
2. Blame the 12-206 cam coupled with a PowerGlide. I have the same combination in my '63 roadster and there is a slight off-idle stumble. Switching to a vacuum can with a lower pull-in vacuum helped detectably. Switching to larger accelerator pump squirters helped detectably. (The engine has an AFB; I bought squirters for the Edelbrock AFB clone.) I've watched the air/fuel ratio in real time and I now know for certain the stumble is a transient lean condition. With the two changes I've made, I can live with what's left of the stumble (and have done so for 14 years). The engine otherwise is very strong and I'm of the opinion the 12-206 is a good cam.
3. When I had the PG in my car rebuilt, the fellow who did the work noted that the kit was missing a cone shaped cushion washer. He warned me it would bang when going from Drive to Reverse (and vice versa). Yep, it sometimes does. This might be the problem with your PG also. The missing washer, as I understand it, would be in the rear of the transmission and would be visible/serviceable by removing the tail shaft housing. So if yours could be missing, you can verify this and remedy it without having to pull the transmission... just the tail shaft housing.
Good luck,
Jim
Frank,
As I read it, you have observed three problems.
1. An intermittent miss, like a dead or weak cylinder.
2. An off-idle stumble
3. A PowerGlide that shifts into Reverse or Drive with an occasional bang.
If I've misunderstood, then just ignore the rest of this posting.
1. The intermittent miss.... the suggestions you've already received about ignition issues make sense. I have nothing to add.
2. Blame the 12-206 cam coupled with a PowerGlide. I have the same combination in my '63 roadster and there is a slight off-idle stumble. Switching to a vacuum can with a lower pull-in vacuum helped detectably. Switching to larger accelerator pump squirters helped detectably. (The engine has an AFB; I bought squirters for the Edelbrock AFB clone.) I've watched the air/fuel ratio in real time and I now know for certain the stumble is a transient lean condition. With the two changes I've made, I can live with what's left of the stumble (and have done so for 14 years). The engine otherwise is very strong and I'm of the opinion the 12-206 is a good cam.
3. When I had the PG in my car rebuilt, the fellow who did the work noted that the kit was missing a cone shaped cushion washer. He warned me it would bang when going from Drive to Reverse (and vice versa). Yep, it sometimes does. This might be the problem with your PG also. The missing washer, as I understand it, would be in the rear of the transmission and would be visible/serviceable by removing the tail shaft housing. So if yours could be missing, you can verify this and remedy it without having to pull the transmission... just the tail shaft housing.
Good luck,
Jim
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