Ever since putting the “new” used engine in the ‘64 for the Opposite Lock Rally, I have been battling a rough running issue. It ran good at the start, then got progressively worse as the day went on, ending up nearly undrivable by the time we got home after the 450 miles.
I found the distributor was hilariously worn, and a new one(which came with a cap & rotor) seemed to fix it, then it got bad again. It would run a little rough at idle, randomly bucking or shuddering a bit, and doing the same when driving. However if I drove for a while it would get worse and worse, ending up with the whole truck shaking and a lot of two-footed driving or messing with the manual choke to keep it running.
I thought it might be the old plug wires (swapped over from the old motor), so I changed those. Then I thought it was the coil, so I put a higher-output Firepower one in in place of the old OEM.. Each time it would run better for a while, then go back to running like crap.
Yesterday I swapped a new points plate & setup in, in case the Pertronix ignition unit was bad, it ran & idled fine last night, but driving to work it started stuttering madly when accelerating below 3K rpms. It was hell getting it home as it kept acting worse and worse.
I decided I needed to start from baseline. So I pulled the plugs to check for a bad cylinder. They were all the same and normal looking. Next I pulled the distributor, found TDC with a piece of welding wire to ensure the balancer hadn’t slipped, and stabbed the distributor back in. I re-assembled everything, set some initial advance and started it. While tuning by ear to something close enough to run, I could feel the distributor was slimy and the wire boots were arcing to my hand. I’d never noticed either of these before. I left it running for a while while checking in occasionally, and low and behold, I found the dumbest cause ever.
The upper heater hose goes on a nipple just above and ahead of the distributor on these old 250 inlines. It had a pinhole leak that, when hot, sprayed water & coolant right on the distributor, causing it to arc all over the place.
I cut & re-attached the hose (new ones are now going on this week), and sprayed the distributor with WD40 (using it for its designed purpose for the first time in my life), and the truck runs amazingly better.