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  1. #1
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default 98 polaris sportsman 500 backfire through carb?

    my quad started running like crap, it idles fine but seems to backfire through carb or something when you give it gas
    I cleaned carb twice, no change
    plug looks perfect, good color and clean
    fuel pump is working, clear filter is full of fuel
    would a bad ignition do this?
    any ideas?
    thanks!

  2. #2

    Default

    Have you checked valve clearance lately? Possible vacuum leak, inspect the carb boot carefully for cracks also maybe bad spark plug cap, they are cheap so maybe just change it, when you do cut a 1/8" off the plug wire before screwing the new one back on.

  3. #3
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    the valve clearance has never been checked
    new plug did nothing
    was thinking of replacing coil and plug wire next

    ran fine but shortly after my 18 year old son rode it out back it started to loose power and now pops and sputters as soon as you give it gas
    I hope he didnt bend a rod or something... it idles just fine, not sure if that would be the case if a rod was bent...

  4. #4
    Join Date
    Dec 2009
    Location
    The Keweenaw Peninsula
    Posts
    2,221

    Default

    I would think if it were a bent rod, the idle would also be irregular. I think what was previously mentioned by dofo1 is a good start, especially the carb boot. Just my 02.-Mezz

  5. #5
    Join Date
    Dec 2009
    Location
    back to cuttin wood
    Posts
    1,227

    Default

    you might have rounded off some cam lobes , check the ex valves to see if rockers are loose

  6. #6
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    Quote Originally Posted by rp7x View Post
    you might have rounded off some cam lobes , check the ex valves to see if rockers are loose
    I am going to do exactly that, starting the tear down tomorrow
    On line it appears that was a common problem, cam, exhaust lifter and gaskets $180 on ebay
    I hope they are all good quality parts.... going to take it appart first
    I saw a post on here last year about the same thing, if you try to pull start it you about rip your arm off sometimes...

  7. #7
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    I ended up buying valves, springs, gaskets with the rockers and cams so I am in $260 and am having a guy grind the seats and put in valves on monday for $40
    It was really easy to get apart, hope it goes together well
    I will try and attach a photo of the old and new cam, look at the center lobe, that is the exhaust lobe!
    Attached Images Attached Images

  8. #8
    Join Date
    Nov 2010
    Location
    Munising
    Posts
    1,326

    Default

    I had these symptoms with a suzuki ltz 400. Hard cranking. Was tied to the carb being jacked up. When it sat liquid gas was flowing in to cylinder.
    essentially hydro locking. When running it was fine except when hammering on it. It would start backfiring and sputtering at times. I did my valves, messed around with ignition, then finally bought a new carb and it is a new machine.

    Hope the cam - valves do the trick for you. But if not, dont over look it possibly being the carb.

  9. #9
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    thanks, but I hope this is it!
    even the day I took it apart I could flip the choke, turn the key and press the start and it would instantly fire and idle, only backfired when throttle was applied
    On line they said it was soooo common it should have been a recall....
    I cant believe I hauled a wagon full of wood the day before she had enough, must have been losing power for a LONG time!



    Quote Originally Posted by snocrazy View Post
    I had these symptoms with a suzuki ltz 400. Hard cranking. Was tied to the carb being jacked up. When it sat liquid gas was flowing in to cylinder.
    essentially hydro locking. When running it was fine except when hammering on it. It would start backfiring and sputtering at times. I did my valves, messed around with ignition, then finally bought a new carb and it is a new machine.

    Hope the cam - valves do the trick for you. But if not, dont over look it possibly being the carb.

  10. #10
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    Fixed and running fine!
    cam def the problem!

  11. #11
    Join Date
    Dec 2009
    Location
    Cloquet, MN
    Posts
    945

    Default

    Let me know if you don't experience the hard starting issue anymore. Where did you get your parts from?

  12. #12
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    Quote Originally Posted by elf View Post
    Let me know if you don't experience the hard starting issue anymore. Where did you get your parts from?
    http://www.enginesourcing.com/
    That is where I got my cam and rockers from, just chose one off of ebay
    Mine has been starting fine with the battery
    I might pull the cover off and check to make sure the spring is in the correct configuration, the guy that did my valve seats put it on...
    I could have skipped the valves, they looked good even at 9k miles but I figured might as well

  13. #13
    Join Date
    Dec 2009
    Location
    MI
    Posts
    522

    Default

    ELF,
    little update, I had the valves done, head checked by someone else and he put the cam in and I never checked the spring and although the quad always started with the battery it seemed like it was struggling. I decided to pull it in, took off the side panel, pulled the coolant line at the thermostat out of the way, pulled the side cover on the cam and he didnt have the spring on correctly. I pulled the decompression valve out a little, set the spring correctly and it starts way better! I would suggest pulling the 2 wheels on the cover side up on a 2x4 or something to reduce coolant loss but it really doesnt drain much out at all and is quick and easy to do, I am not sure that the paper gasket is needed for the thermostat as it has a thick rubber one on the inside but I made one and replaced it anyway....

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