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  1. #1
    SURFnTURF's Avatar
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    Detonation on a 98xpl 951

    My set up is :Group k sleeper kit, water injected by les cooke,rinnaldi reeds amd spacers, proks,stock prop modified,mpem modified by les cooke, compression 140 both bores, stock oil injection,carbys rebuilt and rejetted 170 h/s screws turned out 3/4 turn, low speed 87.5 turned out 1.1/2 turns. fuel lines replaced , fuel filters replaced,1.5mm oversize bores with .005 clearance,rave valves cut back,max revs 7120 , 6 hole base gasket , stock head releif cut for 0.073 squish.Fuel is 98 ron.

    When i installed the flywheel I loosened the front magneto bolts and turned the magneto as far as i could in the direction the motor turns.I thought it might give me a little more push down low, but i think it has started detonating because when you warm it up and then give it to her it sounds like an engine bay full of empty bottles banging around in their.
    I have pulled the motor and have moved the magneto back to its original position I scribed a line on the outside of the ring gear originally so its back to where I had it. The difference in the before and after setting was about 3-4mm in the circumference.

    Do you guys think that might of put it over the edge as regards detonation when i moved the magneto.The reason why I just dont retard it with a dealer programmer is because its already at 8 (max retard )on the programmer.
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  2. #2
    Duke's Avatar
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    Looking at your picture thats about 4 or 5 degrees. Do you know what curve Les programmed your box with?

  3. #3
    SURFnTURF's Avatar
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    Quote Originally Posted by Duke View Post
    Looking at your picture thats about 4 or 5 degrees. Do you know what curve Les programmed your box with?
    No, he did this back in 99 and installed water injection controlled through the mpem,he must of done something with the hour meter in the mpem as well because it only says 149 hours on it.This is strange because this is the first time I have put a dealer programmer on it since the upgrade and it had over 100 hours on it back then.Wierd.

    Anyway if that distance in the picture is 4-5 degrees it would of been way too advanced so now I have loosened the bolts and returned it back to where I had it before the pinging.

  4. #4
    Duke's Avatar
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    Do the 98s have the throttle position sensor or did that start in 99? This gave me fits on timing until I got it adjusted right.

  5. #5
    96XPSS's Avatar
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    Quote Originally Posted by Duke View Post
    Do the 98s have the throttle position sensor or did that start in 99? This gave me fits on timing until I got it adjusted right.
    Started in 99.

  6. #6
    SURFnTURF's Avatar
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    just thought i better update this for other readers, I pulled the motor , pulled the front cover off and returned the magneto to my original position and tested and detonation has gone, it still pulls like a train but obviously was too far advanced. feels good and safe as well.

  7. #7
    96XPSS's Avatar
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    Quote Originally Posted by trevsy View Post
    just thought i better update this for other readers, I pulled the motor , pulled the front cover off and returned the magneto to my original position and tested and detonation has gone, it still pulls like a train but obviously was too far advanced. feels good and safe as well.
    Sounds good...thanks for the update. I've never heard of anyone manually advancing the ignition like you did. Be thankful you didn't hole a piston...

    Happy riding!

  8. #8
    SURFnTURF's Avatar
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    Yeh it was a first for me as well !. I never really held it wot for very long maybe 1-2 seconds but as soon as I heard pinging i would back right off.

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