A friend has a 2002 375 Auto that runs rough when it gets hot. I thought maybe it was the coil, but these things dont have coils do they? It has a magneto, correct? any item in that system that can fail at higer temp.?

fuel problems usually show themselves regardless of engine temp. so I havent ventured there yet.

Any thoughts?

 

Even a magneto has a coil, but this engine has a CDI system (Capacitive Discharge Ignition) and has a box and a coil. First change the spark plug, It's cheap and should really be changed once a year. You can check coil output. Use a used spark plug (a new on will work also) and with engine cold, plug the spark plug into the plug wire. Hole the spark plug base about 7/16 to 1/2" from the engine frame and crank the engine (I usually wear a glove and hole the wire with insulated pliers as even a weak system will hurt if the spark jumps ro you). If the spark won't jump a gap of at 7/16" the ignition has a problem. If good, reinstall plug wire and run engine until warm and rerun test. Spark should still jump the 7/16' of better. If not you need to run ignition system componet tests. Oh yeah, run the test with a spark plug in the engine, so the engine will crank at normal speed.

 

Could be a carb problem...or dirty air filter.
As the motor warms up, it needs a less rich mixture. If someone went richer on the mixture screw, to get better cold weather warmup, it could now be too rich for when the motor is hot.
Change the plug, and if its still running rough, check the air filter and reoil it, then try going leaner on the mixture screw. This only effects the idle mixture.

 

Of all the possible fuel problems, bad or wet fuel id the most likely. First off how old is the gas? Fuel goes bad very fast anymore. As quick as a few weeks. The old spark plug will tell you if the fuel mixture is good or bad and if bad, whether lean or rich. If it is a fuel problem, the most likelyis to rich. Is the choke being pushed clear off, don't laugh, seen it happen. Is the spark plug tip black and sooty. I recently saw a choke (enrichment valve) stick and even with the lever off still dumped extra fuel into the system. I would suspect the coil, plug wire, spark plug or CDI box of this problem the 375 is have before fuel.

 

I failed to mention in the original post the steps I had already taken. The air filter is new, spark plug is new and the fuel had been drained and tank filled with fresh fuel.

When I pulled the original plug, it was fouled by an over-rich condition, that's why i replaced the air filter, it was dirty. The bike bogged under load before I replaced all the above mentioned items. Now it just cuts out after it gets hot.

I will test the spark as suggested by Bear4570 ...

 

One question, did you go with the factory replacement air filter, or an aftermarket one?

 

OEM replacement air filter ...