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Help all two strokers.

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My brother rides a 2001 KX 250. We went riding Saturday and he had some problems. Every time he hit top end of power band the bike sputtered. what could be the cause? Thanks. Tony

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it was fine last week,just started happening, we changed three plugs, one was a racing plug the other two were standard

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i sort of saw the same thing happen on a really old yz200. it was just opposite.. the bottom end would sputter and stuff, and mid-top end kicked in and that thing was a monster.. i know jetting fixed that problem :)

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A friend's 97' CR250 was basiclly doing the same thing.I checked jetting,cleaned the power valve,air filter,plug.Started to ttear it apart,looked into the silencer.The "stinger" portion of the silencer was carbon fouled/packed! It was packed so full of crud it was reduced to half it's diameter! After a good cleaning/repacking it ran like new!

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My brother rides a 2001 KX 250. We went riding Saturday and he had some problems. Every time he hit top end of power band the bike sputtered. what could be the cause? Thanks. Tony

sounds like he's too rich.

1) a dirty air cleaner will cause rich jetting

2) warmer air temps will richen jetting

3) an exhaust restriction will cause rich jetting

4) a clogged main jet will also richen jetting

so,

1) clean air filter

2) pull pipe and burn/scrap as much gunk out as possible

3) repack silencer

4) pull main jet and check that it's clean

IF after you do all this you're still cutting out in the higher RPMs, lean your main jet a few sizes.

PS - is the top end fresh or worked? a worked top end will cause starting and running problems

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sounds like he's too rich.

1) a dirty air cleaner will cause rich jetting

2) warmer air temps will richen jetting

3) an exhaust restriction will cause rich jetting

4) a clogged main jet will also richen jetting

so,

1) clean air filter

2) pull pipe and burn/scrap as much gunk out as possible

3) repack silencer

4) pull main jet and check that it's clean

IF after you do all this you're still cutting out in the higher RPMs, lean your main jet a few sizes.

PS - is the top end fresh or worked? a worked top end will cause starting and running problems

he just replaced the piston and rings, I thought it might be a jetting issue.

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he just replaced the piston and rings, I thought it might be a jetting issue.

it's definitely a jetting issue.

a worn spark plug will also act like rich jetting

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