MF 50 Unknown Shutdown

[SaveMy50]

Gas, Z134, Alternator installed, I had previous posts about hard starting but it's better now (may have been a fouled plug).
Latest issue is unknown shutdown, after running for a bit (> 20 minutes). Can't tell if something overheating (coil, condenser?), but it didn't seems a fuel issue (no apparent fuel bowl issue at the times). Previously restarted by bomb starting after 5 minutes, and it shutdown again after ~ 15 minutes. Last time I let it cool an hour, but then it was a bit hard starting again, but it started. Since alternator install and last carb job, I can idle way down compared to before, but these shutdowns have ocurred while driving, and no real load.

 

[miner09]

Check gas cap. Maybe it’s not venting. I had same problem. New cap and it’s fine. Loosen old one and see how long it will run.

 

[used red MN]

So it was originally a 12 volt system or did you also convert to 12 volt when the alternator was added? If changed to 12 volts was the coil changed to a 12 volt coil or a resistor was added? If not coil may be overheating. Also if alternator was not installed correctly and its output passes through the ignition switch this may also raise ignition voltage.

 

[SaveMy50]

Thanks for responses. Shouldn’t be gas cap, as I just changed to a vented one, and minor gas splash on top of tank I think confirms it’s venting, but I’ll try running loosened.

It was originally a 12 V system, generator based. I installed alternator directly to battery. But I did not change the coil, although I cannot recall if it’s a quality coil or not (replaced it 3-4 years ago when old one died in summer heat during haying).