Miss at idle...

[Wizbangdoodle]

I have acquired a '73 F350 Super Camper Special with a 390. It starts great and when revved, seems to be smooth. Idle has a miss somewhere. Performed a compression test, all cylinders are about 145. Rebuilt the carb, no change. It does have a Pertronix ignition installled by the previous owner. Do these go bad? Is that common? I can't think of anything else that would cause this other than ignition. Opinions?

[cep62]

Welcome to our site.

You can ground out , or pull one plug wire at a time to isolate the cylinder.
It could be a bad wire or cap ,
You can also use a I R thermometer and look at each exhaust manifold port , or put a little water on one at a time . To look for a cool one.
If you find the offending cyl you can diagnose it better.

[Wizbangdoodle]

Thanks for the info, will try all of those suggestions. Seems I used to know a lot of this stuff, but got out of tinkering when life got busy. Now I jumped back in with both feet by acquiring a '67 F-250 a '73 F-350 and a '76 F-150 all in the span of 2 weeks. I have a lot of work to do.

[cep62]

Wow ! If you're not a mechanic now , you will be when you get done with all those projects.
F Y I . The left rear wheel on the F350 might have reverse threaded lug nuts. I had a '79 that did.
It took awhile to figure it out.

[Fraser]

One spark plug could be bad or mismatched, or a bad wire.
Reverse thread lug nuts were used on some 3/4 tons as well, as late as '84. It was a Dana thing, so only affected the rear, look for the letter L on the end of the studs, and on the lugnuts.

[Wizbangdoodle]

I'd better check those lugs, thanks for that bit of info.

Yes, I have a lot of work ahead of me. My plan is to do a mild refreshening of the '73. Repaint and detail the engine compartment. I'll probably sell it to finance the other 2. The '67 is the one I'm looking forward to. It is in the worst shape, but I want to make it my daily work truck.