My father recently purchased a 98 Quadrunner 250 4x4. When he first got it, it would run; however, it cut out intermittently and real bad. It also smokes pretty bad but we can deal with that. Changed plug, rebulit carb, drained old gas, and put on new fuel pump. Now it will not run at all. It will start but die immediately. From what I've been reading, I'm starting to wonder if it could be the voltage regulator. Don't really want to buy one unless I'm pretty sure. He (dad) got ripped pretty bad already by the dishonest former owner. Any ideas?

 

I have the same ATV, if it's the rectifier the only way I know to check it is to have it running so I don't think it's that.
Valves are problaby your problem or spark plug from all the oil it's burning, the carb could be the problem too.
Check your valve lash, intake .007mm exhaust .013mm
my email is diamonbird@yahoo.com and I would be glad to help y'all any way I can.
Y'all might want to get a manual before doing any work on the engine but I can help y'all some.