Still running rough

I haven’t had any luck getting the idle smoothed out yet. I’ve tried basically everything I can think of, along with all the suggestions from over at It’s still shaking, and still surging and jerking while at cruise (though I have a feeling the fix for that is a larger carb jet).

I used propane to check for vacuum leaks—nothing. Propane directly down into the carb—nothing. The spark plug wires’ resistance is between 2800 and 3700 Ohms/foot, which seems to be fairly typical for factory style wires.

To check for possible valvetrain issues, I ran the engine with no valve cover. Nothing appeared out of the ordinary just looking at it. I also checked with a timing light on the valvetrain, and everything still seemed fine. Unfortunately, when I put the valve cover back on after that, I broke a bolt off in the head. I need to figure out a good way to remove that. In the meantime, that’s caused a small oil leak at the back of the engine.

I’m at a loss on it for now. The vacuum gauge bounces around a bit at idle, so it sort of seems like it’d be a valve problem or a vacuum leak—yet everything seems fine. The only thing I can think of is maybe the guides, but I’m not sure if that’d cause an issue with the idle or not.