Well, around here, speeds on local roads and highways are about the same, especially in a truck with a top speed in the 50s.
The 15 mi drive was 45-50. The highway was 50-55.
My mom has two cats which keep critters under control so I'd be surprised if that were the case but it isn't outside the realm of possibility.
I was just thinking maybe the second leg of the journey was a higher speed/higher load condition that made the obstruction more noticeable. But it could just as easily be that the nest moved around enough with exhaust pressure to create a more significant plug up, which promptly cleared itself.
But overall, I think the ignition explanation is more about plausible.
Interesting clues:
1) felt the power draw down for a few seconds
2) it backfired once you let off the throttle
Jerry’s explanation of the coil-to-distributor wire doing something funky fits # 2 pretty well. Dizzy would have been rotating as you let off throttle. But I’m struggling to understand the draw down in power preceding the backfire with that one. Shouldn’t a problem there have created a more complete (even if just momentary) loss of ignition?
Something funky in the centrifugal or vac advance is possible. Weights hang up and don’t advance = retarded timing…this explaining the poor power. Backfire occurs once timing comes back to a natural “happy spot” as the RPM came down when you let off. Then again, I can’t imagine why that would happen once, self correct, and never happen again.
Carbking’s story is a good one. Similar….super-flaky, ignition issue that is dependent on multiple factors coming together.
