Here's where it stands:

Swapped out the coolant sensor (two-wire) for a spare. No change.

Unplugged decel-cutoff solenoid. No change.

The truck runs and opens its choke completely, which is better than my '87 ever did years ago before I knew how to spell 'metric," it seems. When it gets warm - dies. However, if I spray it with a little shot of starting fluid, it stays running for a second. If I continue to shoot little shots, it stays running on that shot, and subsequent shots for a second, THEN it will catch and run by itself for about 30 seconds, then die again unless I shoot more starting fluid.

I tried to swap in my ECU from my '86 auto, but one of the plugs is different. Apparently they are year AND transmission specific.

The only thing I have not done is adjust the idle mixture screw, and I'll also say that you cannot keep the engine running with the throttle when it decides to die. It's going to die, no matter what you do.

I'm going to pull the ECU and crack the case to check for the fishy smell and any leaky capacitors. Just for kicks, I'll first bottom out the mixture screw, counting the turns so I can set it back if there's no result, and see if any change there helps. Wouldn't that be nice.

AZRaider, I did ask what adjustments you had to make with your new carb and you just replied that you adjusted the mixture screw. You didn't mention that it wouldn't run or anything until you did that. That's why I asked, so thanks for the additional info so I can look into it. Is it screw-in for more rich or is that more-lean? Haven't ever adjusted that one before.

Again, this thing does run perfectly until it warms up. You can drive it about a block. The choke opens fully. At some point it just dies. and it's hard to restart. I must admit, I never saw this vehicle fully assembled at any point until we put it together. The top end was off of it when we got it and parts were in a box. I followed the vacuum line schematic under the hood for hook-up. Is everything correct? Hellifiknow, ha ha.

AlphaMale, BIG thanks for all the texting support this morning. You have helped me narrow down quite a bit. I appreciate it.

John B.

From the way it acted on me, screwing it out seemed to make it more lean while screwing it in made it more rich.

Mine was running rich, but as I screwed it out, it cleaned it up. And just to get it started, I had to screw it out a little bit.

turning it inward leans it, turning it counter clock-wise richens it.

You sure yours was running rich? lean will make it stumble. Either way, you enriched it.

I have some experience with smaller (400-450cc) carbureted engines from racing and working on atvs and dirtbikes. They were much more finicky then most carbureted auto engine when it comes to intake, exhaust, and altitude changes requiring carb adjustments and or jetting changes.

Seems to me that problem your having would be more likely to come from a poor fuel supply rather than the carb itself. (partially because the carb is rebuilt) If it were a jetting issue it would run crappy when it was cold and warmed up. I wouldn't expect it to die from an improperly adjusted mixture screw or a choke that didn't function only poor performance. (carbs I have worked on all seemed to fall in the 2 1/4- 2 1/2 turns out on the mixture screw as a starting point)

What has the temperature been where you are during your diagnosis?

I'm not a carb engine expert by any means that was just my long winded way of suggesting you look into the fuel supply and fuel pump.
Have you put a timing light on it?

My timing light got legs and walked off on me. It's close enough to allow it to run for now, though.

I started messing with the idle mixture screw. It does run for a while and is quite difficult to restart, but it sounds like this is the ticket. VERY helpful to know which way does what with the screw. The carb that was on there, the one that came with the spare engine, was 1-3/4 turns out (but the carb was really full of crap and I gave up on rebuilding it), so I'll start with that and probably go out from there.

Appreciate the help, everybody. It sounds like I'm on the right track now. Lucky for me I got out early today so I can play with it for a while. I'll report back later.

John B.

I messed with the idle adjustment screw. About all it does is make it longer between times when it dies.

I'm NOW leaning towards fuel supply. I pointed a flashlight at the fuel filter, which is king of translucent, and I could see air bubbles coming into it. I have already replaced the soft lines from the tank to the hard line and from the hard line to the filter, but am using old spring clamps on the ends. I went out and bought some appropriate sized screw clamps and put them on the soft line from the tank with no change. I'll try to get to the line from the hard line to the filter tomorrow. I'll also replace the soft line and clamps from the filter to the pump.

Could the float level be messing with this whole thing? I mean, it runs great, then just dies. Maybe just for fun I'll shoot some carb cleaner in the fuel line just before the carb in case there's anything left in there gunk-wise from when Guaranteed Carbs did their rebuild.

At least it seems easier to restart now. I'll get this fixed and it'll all be behind me. Just have to take it one thing at a time. If I keep seeing air bubbles I'll pressurize the line with compressed air back at the tank connection, cap off the carburetor end and spray everything with a soap n water mixture to see if I see any bubbles indicating a leak. Not sure how to test the pick up from the tank, but when we put this tank on it looked really like new in there. If I have to, I guess I'd pull it and test it somehow.

Just remember, this is FUN...right?

John B.

Yeah, could be the float or float needle sticking. Maybe the tank pickup is getting clogged or the mechanical pump is going. Was the pump replaced with the rebuild?

Since you're able to keep the engine running with the spray, it's almost certainly a lack of fuel that's causing it to die. Keep checking the rest of your fuel supply system and maybe measure your fuel pressure to make sure that the carb isn't just running out of gas because the fuel pump can't keep the float bowl full.

Yes, the fuel pump was replaced last week. And the tank was, too. Super, super clean.

John B.

Is it possible that the soft line is too soft and collapsing shut? Did the lines get mixed up maybe (not sure if the supply and return are about the same size on that)