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FX850V Troubleshooting

Discussion in 'Chainsaws and Power Equipment' started by lukem, Apr 13, 2026 at 11:58 AM.

  1. lukem

    lukem

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    Got a weird one.

    My FX850V on the ZTR is running rough and down on power...sounds like it has a bad miss and/or fuel starving. I've tried everything I know to do and have run out of small engine knowledge.

    Things I know:

    1. Impulse pump is delivering plenty of fuel to the carb.
    2. It will run, although not great, with the right coil unplugged.
    3. It will not run with the left coil unplugged.
    4. The right coil has plenty of spark to the plug. I swapped in a spare coil and saw no change.
    5. The valve lash in the right cylinder is within spec, so I doubt I have a valve hanging open.
    6. The right plug is blacker and colder to the touch than the left plug when I remove them.

    This is where my troubleshooting ability ends. I know the right hole is cool/cold. I'm having a hard time understanding how this could be fuel related since both holes share the same carb. I guess I could do a compression test to make sure the internals aren't hurt.

    Any other ideas?
     
    Last edited: Apr 13, 2026 at 1:49 PM
  2. lukem

    lukem

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    I did a compression test and both holes read the same. I guess that's good news, but now I really don't know what to think. I guess I'll take the carb apart and clean it.
     
  3. Ronaldo

    Ronaldo

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    It may be getting spark but put in a new spark plug( or two). You could swap plugs around and try that too. My Polaris 4 wheeler started running a little weird and would not idle one day. I figured it was time for carburetor work. Dad said do the easy stuff first and put in a new plug. Fixed it immediately. He cam from a time when replacing spark plugs was a part of a tune up. They last so long these days we don’t think of them.
     
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  4. Horkn

    Horkn

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    Interesting. My buddy's kawi v twin on his JD lawn tractor had a valve hang open that the valve guide insert in the head for a valve migrated out and wouldn't seal with the valve to the face of the head. Kawasaki v twin like this have an issue with this happening. It seems the head/ cooling design allows grass/ clippings/ leaves to sit in there and the grass gets hot spots and this happens. His was running one 1 cylinder and no compression one one. But... You said both cylinders have good compression? So that's probably not it
     
  5. Screwloose

    Screwloose

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    I have a trailblazer with the v twin kawasaki and it sure runs hot. Always worry about the guides walking out.
     
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  6. lukem

    lukem

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    I put new plugs in last year toward the end of the year...and swapped them today. No change.
     
  7. Screwloose

    Screwloose

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    I believe that engine has a 2 barrel carb and it's possible for the solenoid to starve one side.
     
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  8. brenndatomu

    brenndatomu

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    Is the right plug wet?
    If not then it would seem that side is not getting fuel.
     
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  9. Jeffrey Svoboda

    Jeffrey Svoboda

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    Have you tried finding a vacuum leak. Seems I worked on one that would misfire/ backfire intermittently and iirr it had a crack in the intake manifold. It probably didn't run as rough as yours but maybe worth a try?
     
  10. brenndatomu

    brenndatomu

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  11. lukem

    lukem

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    A lot of similarities. I noticed an oil leak and dirty fina on the right side too.

    I'm going to try a good carb cleaning and shoot the headers with a temp gun and make sure it really is down a hole.