Yeah, I know, how many of these threads do we have already??!
I've been reading the archives and picked up at least one thing to try. Here's the situation:
1949 3600, mid '50's 235 with recent valve job and new fuel pump, distributor and coil. 6 month old NOS Zenith 228 that went on right out of the box. My wiring is crap so I've hard wired a wire from the key switch directly to the + terminal of the coil, bypassing the stomp starter.
Truck was running like a dream for the last 6 months since I put the Zenith on. It was a carb that had sat on someone's shelf forever (even came with the Pep Boys receipt from 1970). I didn't think I'd get more than a week out of it before having to rebuild it, but it still looks pristine and all the rubber is fine, ethanol or no.
So, truck was running brilliantly, but getting poor mileage (about 10-11 MPG) so I leaned out the main jet (this Zenith still has the adjustable main). Instead of 4 1/2 turns out (what the manual advises) I turned the jet in to about 2 1/2 turns out. Result was that the truck was more dependent on choke to start, and had a little struggle when cold to accelerate at the bottom (but no problem once past 1,000 RPM). No measurable change in fuel consumption though
So these settings work for several months then the truck starts to demonstrate more of a stumble on the low end and particularly when cold, but would be fine above 1,000 RPM. Suddenly, last week, I go driving off cold, get about 1/4 mile and the engine goes rough and quits. I restart it and 100 yards on it dies for good. Really sounded like fuel starvation but a failing coil does something similar.
On disassembly the carb is spotless everywhere, no corroding rubber. The accelerator pump works like a champ from beginning to end of the stroke. The fuel pump is dumping so much fuel into a jar I suspect perhaps too much pressure? Check the float level and it is 3/16"-1/4" too high so I reset that. Truck still won't start (it wants to but won't). Acts like too rich, but doesn't smell flooded. Points look good, plugs are black but not much build up, distributor cap and rotor are looking nearly new. I spark test and sure enough: very anemic spark. Swap out the coil for a new NAPA 905 (internal resistor) and the truck starts right up with a little choke. Idle is set too low and engine dies, I put a couple twists on the idle screw and start it again. Runs great, nice and smooth. Idle is too high (1,000 RPM) but I let it go for 2 minutes like that to warm up and at about 2 minutes the engine starts to stumble and then dies.
Jon (CarbKing) in a 2014 post mentioned tank vacuum and gas caps as a possible culprit, so I'm going to check that. I did put on a new cap 2 tanks ago and immediately noticed the truck no longer smelled of gas on bumpy roads, but it's driven through 2 tanks of gas with that cap, so . . .
What else am I missing? Another old post mentioned rubber fuel line but I only have a couple inches of that from frame to fuel pump.
