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  1. #1

    2001 Yamaha XLT1200 Knock at idle

    Hey guys,

    I have a 2001 Yamaha XLT1200 that has a knocking noise at idle. It seems to get better(Quieter) with RPM and is also smoking pretty good. I am new to 2-stroke engines so im not sure what is normal but it shakes pretty bad at idle and knocks with a metallic sound.

    Videos are attached of it running and pictures of what I found.

    Could it be bad gas from storage (I added Stabil marine before winterizing)? Something worse?

    This is what I checked so far. No results

    1. Compression is 110-100-110 front to back.
    2. Pulled powervalve cover on the middle cylinder – pictures attached.
    3. Power valves are actuating together
    4. Changed spark plugs – no change in mentioned sound
    5. Checked spark – have spark in each cylinder
    6. No lack in power(That i know of)or bogging
    Any ideas?








    Also, what is that wire coming off of the exhaust? its not plugged into anything....Looks like exhaust temp?


    Please help....
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  2. #2
    Myself's Avatar
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    The jet pump noise is normal. Hard to tell in that vid but engine sounds pretty normal to me. The pv 1200 does make a funny missing/popping/knocking type thing at idle. Wire out of the pipe is an exhaust sensor. It may already have a d-plate and chip. If those are stock pv keepers you NEED to update them. Also if it's still oil injected, do NOT ride it until oil lines have been replaced. They are well known for being banjo string tight and popping off a carb and killing engines.


  3. #3
    Thank you for the response. It makes me feel much better. i was fearing a rebuild. Supposedly this was rebuilt not too long ago. Also, supposedly this ski has the oil system bypassed. I use penzoil marine for a mix as well.

    The PV keepers- are those the wave eater clips everyones talking about? should i do the couplers and clips as well?

    How/What do i check to know it has a D-plate and chip......also what are those...lol im newer than i thought at this.

  4. #4
    Also, What is your opinion on seafoam? There looks to be a good amount of carbon built up on the piston. Would you use it? and how would you introduce it to the ski?

    Thanks again.

  5. #5
    Myself's Avatar
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    If it's premix then no need to worry about oil lines.
    WaveEater is a name brand. Any updated pv links or clips will work...I use the cheapie clips off Ebay, they work fine. Couplers aren't necessary really for a stock machine.
    D-plate is a thin plate with a D shaped hole cut through it. It replaces the cat converter that came originally in the exhaust that's known for failing. Only way I know for sure to check is pull the rear section of the exhaust off and check. When the cat is replaced with the D-plate a chip gets installed where that sensor WAS hooked up. It fools the computer into thinking it's "seeing" the sensor.
    Seafoam is a good product, you would just add it to the fuel. The buildup is quite normal, you're burning oil with your gas.

  6. #6
    Noted.

    What would happen if this is unplugged without the d-plate? just curious

    Seafoam - i Have treated the gas with stabil marine. Is it OK to add this as well? also, would it hurt to just not do it seeing how its got plenty of power as-is?


    P.S. - This ski is way more peppy than i thought i would be. quite fast for 780lbs with only 155HP.


    Also, I have a 1998 GP800 that idles high and when i revit out of water, id does not come back down in RPM. is it normal to not come down(Lack of backpressure)? and where is the adjustment for the idle because it does like 7 mph at idle and my wife is not so into that lol.

    Thank you in advance. You have been a huge help and are obviously a wealth of knowledge when it comes to Skis.

  7. #7
    Here's how to adjust the idle. Not entirely easy to access this on the 800.




    May need to freshen up gaskets around the carb too.
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  8. #8
    perfect. thank you for the feedback. is it ok to do this adjustment out of the water or does it need the backpressure to be accurate?

  9. #9
    Lots of good information . Need help with my 2001 Yamaha Waverunner 1200 suv I just bought with only 120 hrs has a bad piston because the oil hose was crack ? What should I do first ?

  10. #10
    I guess im just gonna sent it on the 800 and adjust it out of the water! Either way, thank you everyone for the good info and the help. priceless info and knowledge.

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