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Polaris 340 issues

This is a discussion on Polaris 340 issues within the Vintage forums, part of the Snowmobiles category; Ive got one for you. We have a 340 Polaris Cobra that was the most dependable vintage we had for our rides until this year. ...

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Thread: Polaris 340 issues

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    Polaris 340 issues

    Ive got one for you. We have a 340 Polaris Cobra that was the most dependable vintage we had for our rides until this year. Fouled a plug on the output side. It will run with fuel shut off till bowls are empty, but the second you turn the fuel back on it fouls the output side plug. So far we have:

    *Replaced plugs with no results (even tried hotter plug on bad side to no avail)
    *switched carb and fuel lines with no results, does not follow carb
    *Compression test 105 on output side, 115 on other
    *Switched coils back and forth with no results
    *Replaced needles and seats with no impprovement


    Plug is wet when you take it out, but using see through tester both cylinders have nice blue spark. You can make it do it every time. We also only use non oxy fuel. Any thoughts? Thanks

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    Quote Originally Posted by Tonybo View Post
    Ive got one for you. We have a 340 Polaris Cobra that was the most dependable vintage we had for our rides until this year. Fouled a plug on the output side. It will run with fuel shut off till bowls are empty, but the second you turn the fuel back on it fouls the output side plug. So far we have:

    *Replaced plugs with no results (even tried hotter plug on bad side to no avail)
    *switched carb and fuel lines with no results, does not follow carb
    *Compression test 105 on output side, 115 on other
    *Switched coils back and forth with no results
    *Replaced needles and seats with no impprovement


    Plug is wet when you take it out, but using see through tester both cylinders have nice blue spark. You can make it do it every time. We also only use non oxy fuel. Any thoughts? Thanks
    I had a similar problem with a one cylinder Kawasaki trail bike. It turned out to be a defective float in the carburetor. It was a hollow brass float that had a small hole in it that allowed fuel to leak into the float, causing it to ride lower, allowing too much fuel into the engine, constantly fouling the one spark plug, If your float is not susceptible to leaks, maybe it just needs to be reset so it shuts the fuel off sooner. Good luck!

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    Good call on the float check. He did say he swapped carbs and the problem remains on the PTO side but it sounds like a thorough cleaning/reset of the carbs is in order. Maybe a problem w/ the fuel pump, a tear in the diaphragm? Weak coil? I know you said nice blue spark but.....
    Polaris...it IS the way out!

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    Coils have been switched also with no change, will look at the fuel pump.

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    Quote Originally Posted by hobiecat View Post
    I had a similar problem with a one cylinder Kawasaki trail bike. It turned out to be a defective float in the carburetor. It was a hollow brass float that had a small hole in it that allowed fuel to leak into the float, causing it to ride lower, allowing too much fuel into the engine, constantly fouling the one spark plug, If your float is not susceptible to leaks, maybe it just needs to be reset so it shuts the fuel off sooner. Good luck!
    After reading what I wrote, I wanted to clarify something which maybe you understand anyway. Since your snowmobile has two carbs, it would be just the float in the carb that feeds the cylinder that keeps fouling. The other carburetor's float setting is probably fine.

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