I have a 250 it is bored out .80 over and having lots of issues I cleaned the carb and reset the float in it as well I have a 90 jet size in it now, The engine will die out if you give it full throttle right from the start throttle down hard and it dies but if you slowly give it gas it will run good and the upper gears runs fine good power just when you are at a dead stop and you throttle down hard it will die out I have been through this carb a lot and can not figure it out. it also has a new plug and I check the fuel lines going to it the air cleaner is clean and looks to be in good shape. Pleas help if you can.

 

If adjusting the pilot screw on the carb doesn't fix it check the valve clearance.

 

Thank you so much I will check that this evening when I get home it has been a on going problem for a long time very frustrating.

Thank you

 

most likely the fuel screw needs adjusted, the main jet is to small or airfilter is really dirty.