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  1. #1
    Newbie
    Posts
    6

    2001 RM250 Jetting

    Hi Folks, I couldn't find this info on the site, but I bet it's there somewhere, so I'll ask...

    I am running a 158 Main, 3rd clip on the needle and 48 pilot. I run 40:1 Syn.

    All was fine for a few outings - some spooge. so I leaned the needle one groove. I have since got a lot more confident and now give the bike some real stick. However, after a good hot lap the engine ping's at tickover and I have trouble stopping it with the kill switch. I guess this is pre-ignition.

    The reeds are good, the piston is in great condition, the plug looks fine, the crank seal on the ignition side isn't weeping, there is a very small carbon deposit on the underside of the exhaust valve at either side...

    What is the cure? Should I go back on the needle groove (richen) and live with the spooge?

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  3. #2
    Seat Tester
    My Bike(s)
    2008 YZ450
    Location
    NOVA SCOTIA
    Posts
    70
    Sounds like your extra fuel was keeping the ignition cool. Something you could try is a thicker base gasket, or just add an extra stock one. This will raise your port timing and lower the compression, just a bit. Sounds like you have done some jetting so I assume that everything is right. Make sure that you use high Octane fuel, 100 or better is recommended. I can only get 91 so I added the extra base gasket. Didn't notice a power loss, and it really cleaned up throttle response.

    Also do a google search for dealer hop up guide for your year bike.

    Good luck. PEACE!

  4. #3
    Seat Tester
    My Bike(s)
    2008 YZ450
    Location
    NOVA SCOTIA
    Posts
    70
    --------------------------------------------------------------------------------

    Sounds like your extra fuel was keeping the ignition cool. Something you could try is a thicker base gasket, or just add an extra stock one. This will raise your port timing and lower the compression, just a bit. Sounds like you have done some jetting so I assume that everything is right. Make sure that you use high Octane fuel, 100 or better is recommended. I can only get 91 so I added the extra base gasket. Didn't notice a power loss, and it really cleaned up throttle response.

    Also do a google search for dealer hop up guide for your year bike.

    Good luck. PEACE!

  5. #4
    Newbie
    Posts
    6

    2001 RM250 Jetting

    Thanks for the reply.

    I have just noticed / remembered that there was a 2-3mm ring of black oil-like stuff around the base of the spark plug. Would it make that much difference if the plug wasn't 'really' tight?

    Yes I know it's stupid to believe I didn't do the plug up tight enough - I have slapped myself.

    One other thing, my reeds don't have the bent metal outer, they just have a bar along the bottom. Are these standard or Boyson? It may help with the jetting.

    Thanks.

  6. #5
    Seat Tester
    My Bike(s)
    2008 YZ450
    Location
    NOVA SCOTIA
    Posts
    70
    YES! If your plug was not tight, there could have been air getting in around the plug, if this happened it would make it lean,or cause other problems.

    As far as the reeds, not sure but I will see if I can find out.

    PEACE!

  7. #6
    Newbie
    Posts
    6
    Problem sorted.

    The plastic water impeller had come off the metal drive screw/knurled hub.

    I guess I just need a new impeller. Is this a common fault?


 

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