My sons '01 300ex has been sputtering and cutting out off and on when we go trail riding. We went to the dunes last month and had no problems. We went trail riding yesterday and it was acting up on and off all day and has done this the last few times we have gone trail riding. When it does happen it comes back to life if he chokes it. It appears to be after going through water so I question if the moisture is effecting the ignition. When it runs, it runs great. If he stays under power it doesn't seem to be a problem. Trail riding, especially with water spots has alot of stop and go. I've checked the spark plug and cleaned out the air filter. Any help is appreciated.

 

mine does the same thing i think its cuz im getting water in my pipe if u letter it run on choke for like 1o minuts it should run fine until the next water hole

 

Sounds like its air or fuel related. because if you choke it , it comes back. Does it only sputter at one throttle opening ..or all throttle openings?

I was thinking it would be water on the spark plug shorting out the spark, in which case, applieing some dielectric grease to the spark plug and boot almost always cures it.
Was the air box dry each time, you checked it. If theres water in there, check the grommets at the front of the air box for leakage.

Another way to troubleshoot it, is start it up in your yard, and then lightly spray the motor and frame, small areas at a time, until it sputters. If its electrical, you should be able to duplicate the problem. Then seal it up with dielectric grease.

Is it posible theres crud in the float bowl? Drop the float bowl and look for grit and crud..im thinking after going thru a puddle, the forces of sudden slowdown, may be jostling the crud around, and they get sucked up into the jets...then when the motor stops, the crud settles back down, only to repeat the next time.

 

I had a 2000 300EX that did the same, what i found the problem to be, was there was dirt in the airtubes off the carb. I took the tubes off and blew them out, put them back on and it seemed to run much better. Hope this helps