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  1. #1
    lukejaeger1's Avatar
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    02 gp1200r backfire

    I've got an 02 gpr that I just put a new engine in. Tried starting it last night and it would idle fine but would die when I tried to rev it up. I pulled the plugs and they looked fouled. I put a new set of spark plugs in today and it started right up. Within seconds it backfired. When it backfired the water box in the rear blew apart. I was wondering if anyone had any idea what would cause this and if it would have caused any damage to the engine, reeds, or the carbs? Of couse I need a new water box if anyone knows where a good used one is.

    Everything is stock except for a d-plate and I switched it to premix.


  2. #2
    Flywheel isnt aligned right

  3. #3
    lukejaeger1's Avatar
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    I think I have if alligned right. As far as I could see it olny goes on one way. If there is another way let me know.

  4. #4
    Altezza01's Avatar
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    check your reeds. you say you put a new egine in but are the reeds new? i had a similar problem so i checked my reeds and they werent sealing ad had gaps like crazy. I replaced the reed petals and problem fixed.

  5. #5
    lukejaeger1's Avatar
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    The reeds looked when I put them in. I put new petals on last last summer. They should only have about 5 hours on them.

  6. #6
    lukejaeger1's Avatar
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    The reeds looked good, sorry left a word out.

  7. #7
    Happily Self-Employed WFO's Avatar
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    usually the only thing that will cause a violent backfire from the exhaust is ignition timing or port timing

    crank maybe out of phase or maybe flywheel bad causing timing to be off

    also, it may be worth it to check reeds again, because the petals are fragile, and may have hurt something when it went boom

    I have several used waterboxes in stock

  8. #8
    lukejaeger1's Avatar
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    WFO - I would be interested in one of your waterboxes. How can I tell if the flywheel is bad or if the crank is out of phase? This is a reman engine from SBT (second one since last August -5 hours on first one before a powervalve dropped). I will definitly check the reeds. It backfired bad enough that it cracked the fiberglass above the waterbox in two spots 6 inches long.

  9. #9
    Happily Self-Employed WFO's Avatar
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    call me

    713-725-8596
    Rich

  10. #10
    lukejaeger1's Avatar
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    Thanks for the for the info last night Rich. You solved my problem for me I think. I checked the phase of the crank. #1 piston was at top dead center and #2 and #3 were both down from the top of the cylinder the same distance. #3 should have been halfway up and #2 all the way down. SBT"s 2 year warrenty is proving to be priceless aside from pulling motors. This will be engine #3 in the past 8 months. Thanks again!

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