Cub stops when hot

I have a 1950-vintage Farmall Cub with a 12v conversion. It has run well for the last 20 years that I have owned it, but this Spring it has a new problem. After about an hour of work, the engine dies like it is out of fuel (sputter sputter stop). Letting it sit for a while allows it to start again, but untill it has completely cooled down, it won"t run long. Fuel flows readily through the fuel line end connected to to carb. Points and plugs changed last summer, oil and filter this spring. Plenty of power in the battery, too. So what? Could this be a coil problem? Does the carb need rebuilding (last donw maybe 10-12 years ago)?

=Vic=

Could be the coil but check the screen in the carb inlet.

Feel the coil to see if its hot when the engine quits. I would replace the condenser since they're not costly. That screen behind the tube fitting where your gas line connects is sometimes overlooked. Hal

When it stops check the spart then repair as n eeded as its probably your coil. If it runs for an hour it sure isnt gas.

Yes, the coil is noticeably hot when the engine quits. is that a sign of a coil problem?

=Vic=

Went though this same thing with a Cub years ago, I would have bet any amount of money it was the coil, well replaced the coil and still same problem ended up being the inlet screen.

The next time the engine stops, immediately check for spark using a "jump gap" tester. The spark should easily jump a ¼" gap if all is well.

You may have a blocked gas cap vent which would take some time to show the symptom of running out of gas. The next time the engine stops remove the gas cap & see if the problem persists.

i'd say its the coil

The fuel inlet screen may be plugged. Remove the plug from the bottom of the carb and fuel should run out. Even if it does it wouldn't hurt to check it. Remove the fuel line and the brass fitting that it screws into. There's a fine screen behind it. It probably needs cleaning if it hasn't been done for awhile.
Another strange thing on my cub. The air inlet pipe was so cake with old dirt and grease it just barley had a small hole thru it.

I would try another coil. Hal

Coil is breaking down when it gets hot.

Hi well my 49 cub stopped this spring.checked the mag coil and it was was the original and shot.

That is it. Put a 12 volt coil for use with no external resistor if it has no resistor, Use a 12v coil for use with an external resistor if it has one. (usually an attachment near the coil with the coil connected to one side and the ignition switch the other. Jim

Follow up on this issue...

I did replace the coil, but that made no difference (the new coil gets hot, too, for some reason). Fortunately, I needed a coil for an old "74 vintage GMC farm truck, so nothing lost there.

I noted the inline fuel filter on the Cub would be empty when the engine quit, then slowly refill as it sat with the engine off. However, if I pulled the fuel line off the filter outlet, fuel would flow freely. Next I took the carburetor apart and cleaned it, replacing the gaskets. Again, no change, and the cub would still starve of fuel when hot. On one stop I noted bubbles in the fuel filter and suspected vapor lock, but wiggling the fuel lines (which never leaked fuel) would change or stop the bubbling. Now suspecting an air leak, I replaced the fuel line and eliminated the inline filter (OEM never had one, anyway) and while working the tractor in very hot conditions yesterday it never stopped or hesitated. I think the seal around the filter (no clamps on either side) must have gotten bad when hot and allowed air to get sucked in, creating, in effect, a vapor lock condition without actually boiling the gas. So, now one less item to service and, hopefully, many more years of use.

=Vic=

People so often put inline fuel filters on things, thinking they're doing a stroke. They usually cause more problems than they fix or prevent.

Remember these tractors have operated for up to 65 years with nothing more than a piece of glorified window screen for a filter.