Boring, porting, and pipe! Jetting question.

Discussion in 'Dirt Bike Mods & Maintenance' started by Cole Preston, Nov 5, 2016.

  1. Cole Preston

    Cole Preston Rookie

    Nov 5, 2016
    Likes Received:
    I have a 2000 kx250 that i blew the main bearing on last season. I have now torn it apart and am in the process of rebuilding it with a new crank, rod and piston assembly off of Ebay. (Wiseco rod and crank, namura piston). Anyways, the bike already has an fmf fatty and powercore silencer and has a 52 pilot and a 160 main jet. I have the cylinder in the shop right now getting bored slightly (new piston is going to be a 67.35mm stock piston was a 66.35mm) and am having a very mild porting job done to it. I am wondering what jet sizes you guys would recommend to go with?

    Ps-I blew the main bearing going wide open on the lake bed racing my buddies yz250. I'd rather foul a plug once in awhile than risk blowing it up again because this rebuild has gotten pretty damn expensive. Prior to blowing it up, the jetting seemed pretty spot on and hardly ever fouled plugs.



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    #1 Cole Preston, Nov 5, 2016
    Last edited by a moderator: Nov 6, 2016
  2. jaguar

    jaguar Subscriber

    Jul 29, 2000
    Likes Received:
    slight changes like that usually don't require jetting changes. Just make sure you do regular maintenance on your air filter so no dirt comes in to destroy your bearings.

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