Ford 640 running poor after it warms up

Hey guys. I'm new to the forums, and new to tractors. I recently purchased a 1957 Ford 640, and I'm having a little issue with it and haven't found much help. Was hoping someone here may be able to offer some advice.

The tractor will fire up immediately and run great after starting up. I notice it slowly starting to run worse as it warms up though. Runs great for first 15 or so minutes, then it slowly starts idling worse and almost sounds like it's skipping/sputtering. At this time, I can actually pull the choke for about 3 or 4 seconds, and push it back in and it'll clear up, maybe for about 5 minutes. Then around the 30-40 minute mark of working, it actually sounds like a lawn mower when it's running low on gas, and will even shut off. Sometimes I can get it to crank back up immediately (still sputters like it's out of gas), sometimes it needs to cool down before it will crank back up. If I let it cool down for about 15 minutes, I can fire it right back up, and work on it for a while before it's starts acting like it's needing gas again.

We have replaced the gas tank (old one was rusty), rebuilt the carb, new plugs/wires, new points, new condenser, and new resistor.

It's a 12v conversion.

Any thoughts or ideas?

I'm new to tractors, but have a few friends who are trying to help me resolve this issue.

Thanks guys!

Somebody else had the same trouble with one a few years ago. Somebody had put an inline gas filter on that one and it was vapor locking. I told the guy to take it off and splice the line back together. He did,and he said that solved it.

Remove the valve cover and check the clearance gap on the valves. I'll bet the clearance is too small, and becomes even smaller as the engine warms up.

sounds fuel related to me.

pulling choke making it runs better tells me it surely ain't valves!

Sounds to me like you have a coil or condenser problem. When they go bad they work til they warm up then act up just like that, frequently pulling the choke will help for a while. I would try the condenser first, then coil.

12v conversion thats the place to start check voltages does it have spark when it dies it is not a fuel problem if it runs that long unless your fuel cap vent is plugged mite want to blow it out with air. Usually when an engine runs that long before problem its either coil or condenser providing there is still gas running out the drain when removed from carb.

The problem sounds fuel related being that a partial choke improves the running.

Some things to check:

Try loosening the fuel cap. Could be air locking, drawing a vacuum on the tank as fuel is used/temp changes. Don't trust a cap just because it says "vented", sometimes they are not.

I doubt it has a fuel pump, but check it if so equipped.

There is a plug in the bottom of the carb. Try removing the plug, with the fuel valve on (idling if it has a fuel pump) catch what comes out in a clean glass. You should get a full flow until the bowl empties, then reduce to a steady stream. If it slows to a drip or stops, the fuel is not getting into the carb. Check for restrictions up stream, there may also be a screen in the carb fitting where the fuel line attaches. Also look at what came out, is it clean? Water? If it's cloudy or gritty the carb may need the bowl dropped and cleaned.

Check the fuel line. It should be steel, not copper. It needs to be routed as far from the exhaust as possible. If it is a gravity flow system no paper or bronze filters. You can add a screen type if needed.

I think it is a fuel delivery issue, but poor spark can require more fuel to ignite.

How is the exhaust routed?

I fought the same problem on a 971 Ford for five years at a local public school. We tried everything that's already been mentioned by others, plus more. Nothing made any difference. We finally concluded the location of the muffler relative to the fuel lines was causing the fuel to boil in the line.

I quit that job about then, and shortly thereafter the school got rid of the tractor, so I don't know if it was ever resolved.

Vapor lock. Insulate or reroute the fuel line. Move muffler out from under gas tank, too much heat under there.

Bad condenser. But I'm not familiar with 12v conversions. Did it get the resister or special coil so as to work with 12v?

Bad coil. Put it on a wood blochpk an inch farther out from the engine. Use longer bolts make sure they ground it! Those coils get too hot in
their location.

Worn shaft on the distributor. Or worn gears. Something lets it turn sloppy, worse when hot and fumes push up past the worn shaft.

Paul

Did you have it running before you did all the improvements?
Intake manifold vacuum leak comes to mind, but probably not!?

Take the fuel line off at the carb,and let it drain into a container.See that you have a solid flow for several minutes.If your carb has a drain plug on bowl,pull it first,and let it drain.That will prove out the needle and seat,and the fuel line.Mark

Hey guys. First of all thank y'all so much
for the advice and thoughts. We'll try a
few of the things mentioned.

I too think it's fuel/heat related. No fuel
pump, it's gravity fed and I was curious if
the fuel may be getting to hot as well. I
think our next try will be rerouting the
fuel line as a few of you suggested and go
from there.

We have replaced the condenser, coil, and
resistor (although I forgot to mention coil
in the original post).

Thank y'all, I'll update once we get a
chance to get back on it. Preciate the
excellent feedback!!