My wife has a 03 250ex. About 5 years ago, I got a free Big Gun Race pipe and installed it with the recommended jetting. It ran ok but decided it was too loud and after about a year, put the stock pipe and rejetted. I never got it to run right but it did run and then we had kids so it sat in the garage, I never really dialed it in. About 2 months ago, I took the carb apart, cleaned it up and put it back together. I started right up and ran as good as new. I took it to a friends property and it wouldnt start. It sat for another 2 months.

Today, I took the carb apart again, cleaned it and reinstalled. It fired right up. I adjusted the idle and went for about a 1/2 mile ride in the neighborhood. It ran great. I stopped in the driveway and it died. It will start with the choke on but it sputters then dies. It will not start with out the choke. It seems to run hot too. I have also adjusted the screw in front of the carb bowl (pilot jet?), same results. I have no idea what to do next. Any Ideas?

Thanks in advance.

 

Valve adjustment? Worn Rocker arms? When it runs, does it make any tapping noises?

 

Well everytime you clean the carb it runs "great". I would clean the carb again and put a fuel filter on it. I would also clean out the tank.

 

Thanks for the replies. I have cleaned the carb again. Reinstalled and had the same results. I start it up, it will idle fine, I can ride it for about a 1/2 mile then it dies, like it isnt getting gas. I am pretty sure gas is getting to the carb. I pulled the hose off the carb and gas freely pours out of the fuel line. I have always used fuel filters on my bikes after a bad experience years ago, it is clean.

When it runs, it runs like new. No sputtering, no engine tapping, no backfiring. Then it dies. I am stumped.

 

Check the gas cap breather tube. If it is not working, the engine will do what you are describing. Analyze it putting the cap on loosly and riding it. If it runs good, get a new cap or fix the old one.