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  1. #1
    gp1200270's Avatar
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    97 gp 1200 backfires on startup only

    Hey everyone,

    So i am new to this forum but have been working on skis forever.I have to say I am stumped and need some help. Heres my issue.
    I have a 97 gp 1200 non pv. Last season my ski would backfire only on startup. After that it would run fine.I ran it like that for about a year.Then i fried my # 1 piston.Long story short I decided to replace the motor because after said and done I would of been into it for around $1000.
    So i replaced the motor,all new gaskets,new reeds,plugs,fuel filter,fuel lines,battery.The carbs were rebuilt and rejetted about 2 years ago from Oside Bill.So i know the carbs are good.I did to be safe check the filters inside the carbs.All is good right?

    After the motor install I started her up and its still backfiring.I am stumped and I really dont want to take a chance of running it until it is fixed.
    Ski is premixed 40:1,aftermarket reeds,k&n filters,other than that it is stock.Plugs are gapped where they should be.
    Only thing I am not sure of is the water box.I did pull out the water box to check but I am not sure how to tell if it is bad.Water does come out.
    Any help on this guys will be great.Thanks


  2. #2
    Yamaha artisan Cutlass's Avatar
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    If it backfires through the intake, then its probably the reeds. If it backfires out the exhaust, then it could be a carb/fuel system issue. Maybe the needle/seat is leaking.
    Could also be an air leak causing a lean condition and backfire.

  3. #3
    gp1200270's Avatar
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    Thanks cutlass.I think I am going to pull the carbs and double check the reeds.It could be possible they are not 100% seated.I will post back soon.

  4. #4
    Yamaha artisan Cutlass's Avatar
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    When opened up the carbs before, did you take a close look at the check valves. They like to crease occasionally and cause problems. I'm not sure they cause a backfire but since you right there, might as well check that and do a pop off test to make sure the needle/seats are sealing ok.

  5. #5
    gp1200270's Avatar
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    Yeah i checked the check valves.They look good. Oside did this rebuild back in Sept of 2011.Come to think off it I replaced the reeds when the backfiring started thinking that may be it along with the reed and carb gaskets.But I still have the same backfire.I am going to do a pop off test soon.Should be around 55 if I remember correct.I am leaning towards the needle/seat.Do they go bad after a certain amount of hours.I would say I put about 40 hours on the carb rebuild.Thanks cutlass

  6. #6
    gp1200270's Avatar
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    Cutlass i ordered up a pop off pressure gauge today.Once that comes in I will test the pop off.I wanted to get your advice.I started the ski on the hose today and looked into the throat of the carbs.All three carbs had the same stream of gas coming out of the bullseye.If any of the needle and seat were bad would this cause a different flow of gas?
    Thanks man.

  7. #7
    Yamaha artisan Cutlass's Avatar
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    At idle, no fuel should be coming out of the venturi (bulls eye).

  8. #8
    gp1200270's Avatar
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    Yeah no fuel comes out at idle.only when giving throttle.

  9. #9
    Yamaha artisan Cutlass's Avatar
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    Ok good. Well, I'm thinking the NS are probably ok. You say the carb rebuild has 40 hours on it, but did Bill put new needle/seats in? Also what kind of aftermarket reeds are you using? Maybe they aren't sealing on that 1st start up, but after flexing around a bit they seal up better. IDK, just thinking out loud. that might not even make sense...I need some coffee.

  10. #10
    gp1200270's Avatar
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    Oside put new needle/seat in.1.5.I am using boysen reeds.I am going to take a closer look at the reeds while the carbs are off.I will still do a pop off test.Its just weird because it did the same thing with the old motor.I feel it has to be the something with the carbs or the reeds at this point.Just frustrated.I am pounding a coffee myself.

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