Driving home tonight. Truck has sat for about a week or two, ran fine a month ago when I was driving it everyday, and has run fine since even though it's been more or less sitting, but it's been started and run for a few minutes every weekend for the past couple of weeks. Fuel was basically empty.
Tonight I filled it up to about 3/4 and was driving up to Golden (~50 minutes). Running on the interstate at about 60-70 that whole time, running great, making great power, smooth, then I got onto I-70 West from I-25 north. I had gone through just under a 1/4 tank of the new gas (85 octance, which it has run for 2 years with no problem). There is a small hill there, and I immediately noticed a lack of power, but it wasn't just the hill, there was something not running right with the engine, it was immediately dogging down to 50 on just a slight incline. Once I got on the flat I couldn't get it to pull above 60mph and then it started hesitating like the brakes were sticking intermittently or something. Then on a corner the engine quit for a split second (my Lockright made the truck lurch pretty suddenly) and then starting running again, but getting rougher. So I was getting close to Wadsworth and it was running pretty rough with no power, so I shut the engine off and coasted to a stop. Tried to get it started again, didn't want to start so I waited for a minute and then it started again, but I have to keep it revved up to keep it running and it runs really rough. Made it to Treeroot's house, and made some diagnostics.
This is what I've checked - 10/76 FJ40 with stock engine etc.:
-No oil leaks anywhere (oil pressure is good)
-All vacuum hoses that had previously been hooked up are still hooked up (checked multiple times)
-All wiring at the carb (I think) that used to be there (though not complete I don't think, the truck ran fine with/without it) is/was still there, as far as I could tell. Don't know what most of it does or would do if it was hooked up...
-Dizzy looked fine on inside (electronic '78)
-Glass bowl showed good level of fuel in carb even while running (not starved before it reaches the carb)
-Primary barrel has plenty of fuel being squirted into it (not fine mist, kinda "droplety," but that shouldn't make the truck run rough should it?)
-Secondary barrel doesn't look like it's ever been used, but I don't think that has anything to do with this. That's a separate issue.
-Plug wires all tight. Pulled them one by one with the engine running, the only ones that made any difference to the way the engine ran (engine speed slowed down) were #3 and #4 (made engine drop in rpm). Unplugging 1,2,5 and 6 (one at a time) didn't change the way the engine ran at all. What?
-All plug wires arcing to plugs, so the plugs are getting voltage and should be firing.
Yeah so don't know what else to check. Thoughts on what might be wrong?
-Something jammed in a jet in the carb, or fuel not being misted causing problems.
-Bad fuel? Should I get fuel additive and see if that helps?
-It happened pretty suddenly, but I couldn't find anything that changed. So either electrical or fuel related I think. But what changed?
This is my only vehicle until my red truck gets a new timing chain tensioner, so the sooner I can get this fixed the better.