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2015 KTM 250sx proper jetting and fuel ratio

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So I am a fairly new owner of a 2015 KTM 250sx. The bike ran good for a while with a 50:1 mix which is what the previous owner used. The manual reccomends 60:1. However, recently i have been fouling the recommended spark plug and believe it has to do with jetting. The bike also tends to smoke a lot more than i think is normal as it leaves behind clouds. I cant seem to get a good understanding of the idea so i was wondering what any of you guys could do to help. I ride motocross and trails mainly in pennsylvania and places -1000 sea level.   All i know is that there is a 158 main jet in. I have not done any digging yet because i don't even know where to begin with figuring out what jets to use.

Any recommendations or solutions would help.

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 Well there’s a lot to be said here first of all be sure he reeds are in good condition.

 I am of the opinion that the 60 to 1 ratio just reduces smoke and makes the tree huggers happier.

 I am a 40 to 1 guy.

 OK onto jetting the factory n1  series needle in that motorcycle is junk it needs to be snapped in 2 and thrown into the aluminum scrap pile..

 The SX bike has a richer 6.5 slide whereas the W and the XC models have a leaner number seven slide .

 With that being said I would recommend a Suzuki RM needle, there are many to choose from, some will say necj ,

 But that needle has always been far too lean for me go richer like  NECH or NEDH  and go up on the main jet that 158 is too small try 168 up to 172 

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letting it idle too long?  using outboard oil ?  right crank seal sucking trans oil ?  even if it's a little rich they usually don't foul plugs.

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