3400 3Cyl Gas stalls when engine hot

Experienced mechanic here but a little stumped. My Ford 1973 3 cyl gas tractor began stalling and only idles with choke full on. When she cools down it runs full power until engine heats up again.

Ignitiona system fine, fuel clean, fuel filter good. Had myself a can of butane in the tool box and used that as a starting aid when the problem occurred and engine ran. So diagnosis is confirmed fuel starvation problem.

Step 1 removed carb, cranked engine and observed fuel pumping out line.

Step 2 dismantled carb, accelerator piston thingy seemed to be sticking, cleaned up. Float and needle seemed to be free, checked jets, and blew air through passages, reassembled.

Step 3 Ran the Tractor for about an hour moving some gravel and starvation problem re-occured.

Step 4 Retraced all fuel lines, nothing touching block or appearance of vapor lock condition.

Step 5 Scratch my head and post here, what do you all think? I have seen mechanical fuel pumps with cracked diaphragms do similar things in older cars. Not sure if the fuel pump has that same design on a Tractor. Another thought might be float needle sticking, any advice welcomed.

Thanks in Advance

I'm no expert on these gassers, but have gotten some experience this spring on a 5000 gas. Start with the cheap/easy fixes first. When you say the fuel filter is good, is that an aftermarket canister type? They originally had screens - one in the bottom of the tank, another in the top of the fuel pump, and a third at the carb. There is a diaphram in the pump that could crack, but I'd think the problem would be consistant if that was the cause. I'd suspect trash on one or more screens.

Yeah the filter is a canister style inline filter, I put it on a few years ago. I can see screens and such causing fuel starvation but the problem is consistent with max engine operating temperature only. If screens were partially plugged I think it would happen all the time.

Thanks for the post

Ok, here is the fix for all you future Ford 3400ers pulling your hair out and doing silly things suggested of other sites like replacing distributor bushings.

Here is what I found, the fuel pump deliver was inadequate. The tractor would run great for about 30 mins. then stall and only idle with partial choke. Let it sit all night and you could start all over again.

The fuel was gravity bleeding back into the carb over night, when you first started it, the 30 minutes of run time were due to the full float bowl of fuel.

So what I found is there are several problems that could occur with fuel line inline filters fittings. My suspicion is a worn cam lobe and pump not moving enough volume since i blew through my lines with compressed air.

So I went to the auto parts store and bought a 3-4 lbs electric pump for about $40. Removed my fuel filter and ran the pump right out a gas can into carb. No stalling when hot anymore, by passed the whole old system by installing the new electric pump between tank and carb....fixed.