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fouling plugs. 2001 yz250f

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my old 2001 yz250f has just started fouling plugs. i didnt ride it for a while and when my did went to start it the other day it wouldnt go. we changed the plug and it ran fine. we took it for i ride and it was fine. then today we went to the track and when he went to start it it didnt run. so we changed plug and it was fine. why would the plug foul with one hour on it. could my dad be starting it wrong? he does give it a bit of throttle when he starts it ( old 2 stroke habbit) would this effect it? do you think there is any other reason why its doing this? when we took the old plug out the tip was black.

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my old 2001 yz250f has just started fouling plugs. i didnt ride it for a while and when my did went to start it the other day it wouldnt go. we changed the plug and it ran fine. we took it for i ride and it was fine. then today we went to the track and when he went to start it it didnt run. so we changed plug and it was fine. why would the plug foul with one hour on it. could my dad be starting it wrong? he does give it a bit of throttle when he starts it ( old 2 stroke habbit) would this effect it? do you think there is any other reason why its doing this? when we took the old plug out the tip was black.

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Most likely the rings are shot. Time for a top end freshening.

It could be a plug issue if the gap was way big though you said you've replaced the plug so I want to assume you check plug gap on install.

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i dont think the rings are shot. it still has plenty good compression. although i do have some spare rings. would i just be able to pull it apart and replace them or would i have to do any thing else like valves or piston aswell.

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thanks for the link but i know how to start it just dad doesnt. he has always ridden two strokes and now he rides my old yz250f he gives it throttle just on habbit

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Fouled plugs on a 4S are caused by a too wide a plug gap, worn rings and once in a 'blue moon', valve seals. Jetting does not magically change and you make no mention of running issues.

Clumsy starting will not do it unless you start the bike, run it for five seconds, shut it down, restart it in ten minutes and repeat that all day.

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when i pulled the plug out the tip was black. how do i check the plug gap? what should the gap be? i have not changed the jets. the bike still has good compression, how could the wrings still be leaking oil?

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