REPLACED THE SPARK PLUG, started RIGHT UP, did NOT IDLE STRONG, ADJUSTED AIR FUEL GOT BETTER THEN DIED OUT. WOULD NOT START AGAIN, REPLACED AIR FILTER AND IT STARTED RIGHT UP, AND THEN DIED OUT AND CAN NOT SEEM TO GET IT STARTED AGAIN, ANY IDEAS?

 

so if I am reading this correct you said replaced spark plug and it started right up then died out then replaced the air filter and same thing common ground here letting it sit for any length of time and it starts up? I would lean towards carb issues flooding out or not building pressure to keep it running

 

i have a similar case i am working on a 200 honda trx 300 fourtrax would crank and idle great but as soon as you give it gas would die. prime the carb it would run like a tip. figured jets were clogged up cleaned carb, replaced plug, crunk and done the same thing. went through the carb again and now it won't even try to crank just backfires everynow and again any ideas????

 

I've never worked on a 300, but I'm thinking they have an electric fuel pump. Have you checked to make sure you are getting full fuel the the carb? I'd just open the carb drain screw and turn on the fuel pump and see if fuel will run out of it for a little while.