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HollandWR426

Attempting BK Mod/ Jetting this weekend, need advise

5 posts in this topic

I found some good posts on step by step instructions for the BK Mod but have a question regarding the jetting. My bike has the throttle stop removed, BD baffle, and airbox baffle removed. Stock Jetting. I think my mixture is a bit lean due to the semi-opened exhaust and intake so I was thinking about moving the needle up one position. My question about the BK is, Will one position up be enough/too much or will I need to go up 2 since I think the BK also leans out the mixture? I ride in western Michigan at 610 feet above sea level. Any advise would be appreciated. I don't have any other jets than what came with the bike. Current symptoms are "jerkyness" at 1/4-1/3 throttle. Everything else is fine, starts, etc. My ultimate goal is to clean up the jerkyness for when I am cruising on the road.

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The GB/BKmod reduces the timing/duration of the accelerator spray at bottom only.

Becouse it is limiting the amount of gas that is injected from the pump yes you are correct it will lean this out a tad at Bottom only zero to 1/4 or less.

Chances are you will be ok on the PAJ or Pilot Jet.

:) Good luck

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I found some good posts on step by step instructions for the BK Mod but have a question regarding the jetting. My bike has the throttle stop removed, BD baffle, and airbox baffle removed. Stock Jetting. I think my mixture is a bit lean due to the semi-opened exhaust and intake so I was thinking about moving the needle up one position. My question about the BK is, Will one position up be enough/too much or will I need to go up 2 since I think the BK also leans out the mixture? I ride in western Michigan at 610 feet above sea level. Any advise would be appreciated. I don't have any other jets than what came with the bike. Current symptoms are "jerkyness" at 1/4-1/3 throttle. Everything else is fine, starts, etc. My ultimate goal is to clean up the jerkyness for when I am cruising on the road.

Since your motor now breathes and operates like a YZ motor, have you thought about trying YZ jetting? All you need to change is the needle. Not the clip position, the YZ has an entirely different needle. It is probably the best twelve bucks you can spend on your bike. Most YZ owners are much happier with their jetting than WR owners, who have to deal with wacky jetting necessitated by a choked up engine.

That jerkyness is your engine starving for fuel due to having the wrong needle in there.

Hope this helps.

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Yeah, the OBELN needle would probably work for you. It's a YZ250F optional needle...(My Canadian OBEKN is half a clip shorter; richer.)

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Ditto on the OBELN. Made a big difference for me, and only costs $12.

:) <--- been meaning to use that!

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