MF35

Got a mf35 that 4 yrs ago ran great plenty of power until it dropped a
valve didn’t damage any parts other than valve. Six months ago I
had the head completely worked and installed onto tractor. Over the
past 6 months I have completely reassembled tractor, rebuild
carburetor. Now the tractor runs great but after awhile of using the
engine will studder one or twice and shut off. Let it sit 5-10 min and it
will start back up. Checked fuel delivery and carb is getting plenty of
gas. Exhaust does get extremely hot but it always has. Thinking for
some reason the tractor is vapor locking but not sure exactly why.
Any help would be greatly appreciated thanks

Going to have to catch it in the act and move fast!

As soon as it fails, check for spark. Have a spark tester (an old plug with the electrode bent out or broke off). It should jump 1/4" at the plug end of each wire.

If loss of spark, feel the coil. If it is uncomfortable to hold, noticeably hotter than the surrounding engine components, it may be failing, or the wrong coil.

Also check the power to the coil, turn and wiggle the ignition switch, see if the power drops.

And check the point gap, check for side play in the distributor shaft, try an old condenser.

If all that checks out, run it again until it quits, be ready to quickly pull the drain plug on the carb bowl. It should have a steady stream of fuel. If it slows to a drip, or stops, there is a delivery problem.

There should be a screen in the carb inlet fitting, one above the sediment bowl, and one inside the tank.

If there is an inline filter, that can cause fuel delivery problems. Paper filters don't play well with gravity flow systems.

Try loosening the gas cap. Even though it may say "vented", don't trust it. The vent may be clogged, or the cap labeled wrong.

As for vapor lock, if the fuel line is routed too close to the exhaust, it may well be vapor locking. Try moving the line as far from the exhaust as practical. It should have a steel line, not copper. Copper is more conductive and more prone to vapor lock.

Check the distributor centrifugal advance and the initial timing. Retarded timing raises the exhaust temperature.

I think that is supposed to have a heat shield between the engine and the fuel tank. It needs to be there to keep the gas from boiling in hot weather and under heavy load.

Hope this helps, let us know...