Results 1 to 9 of 9
  1. #1

    Help : SL 780 misfiring on PTO cylinder

    Hi, my SL780 misfires on the PTO cylinder at higher speeds, low speed is fine. The other two cylinders run just perfect. Have checked plugs, igntion spark, carb (disassembled, cleaned etc), fuel supply ok, compression ok etc. The moment you open the throttle, it starts missing, plug wash is sooty (thus getting fuel, no spark?). I decided to test the coils and they are ok in terms of resisitance, igntion cable ok, BUT the on the PTO cylinder the spark plug cap resisitance is only 4,2k ohm, the other are just over 5k ohm.

    My thinking is that the resistor in the cap may be "leaking over" and at high speed just flashes over and the CDI unit does'nt like it. I live far from water to do practical testing, so need to be quite sure it's sorted next time I travel to a lake. Has anyone out there experienced something like this or have experience of this ? How sensitive are the CDI's when the total resistance becomes too low. The plugs are BR8ES's. Thanks !


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,596
    +1
    1,276
    Quote Originally Posted by martinv View Post
    ...I decided to test the coils and they are ok in terms of resisitance, igntion cable ok, BUT the on the PTO cylinder the spark plug cap resisitance is only 4,2k ohm, the other are just over 5k ohm.

    My thinking is that the resistor in the cap may be "leaking over" and at high speed just flashes over and the CDI unit does'nt like it. I live far from water to do practical testing, so need to be quite sure it's sorted next time I travel to a lake. Has anyone out there experienced something like this or have experience of this ? How sensitive are the CDI's when the total resistance becomes too low. The plugs are BR8ES's. Thanks !
    Are those the exact model spark plugs spec'ed by Polaris for that engine?

    Edit; There is resistance in the plug caps, and inside the spark plugs.

    Be sure all the spark plugs are properly gapped. If you have not done so already, put in new plugs, of the correct type.

    Your problem could be caused by a loose electrical connection, or by the CDI module starting to fail, or possibly the stator.

    Is there no water near you, where you can back the trailer and boat into the water, and test the engine under load with the boat strapped to the trailer? Even just a pond will do, as long as you have permission, and trailer access.
    Last edited by K447; 10-07-2007 at 11:07 AM.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Location
    Cleveland OH
    Posts
    17,330
    +1
    31
    The spark plug boots do have a 5K resistance. Try the new plugs as mentioned. Try swapping plug wires if you can and see if the misfire follows. Also you can buy just the plug boots. Oh, and try removing the plug boot and cut the wire back about 1/4" to get a better connection. Then rescrew the boot back on and ziptie it.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,596
    +1
    1,276
    Quote Originally Posted by xlint89 View Post
    The spark plug boots do have a 5K resistance. ...
    Oops.

  5. #5
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
    Join Date
    Aug 2006
    Location
    Pittsfield, MA
    Posts
    3,350
    +1
    26
    You had the carbs off. Did you by chance take the manifold off and check the reeds on that cylinder? Just curious

  6. #6
    Hi Guys (and gals)

    Thanks for all the replies and help, I checked all the stuff you mentioned. I took it to water today and still had a "black" spark plug on the PTO cylinder. I eventually disconnected the gray wire I read about and whalla. I now need to determine why it is in limp mode, no obvious reason. Fuel OK, Oil OK. Any ideas ?

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Location
    Cleveland OH
    Posts
    17,330
    +1
    31
    The other reason limp mode will come into play is overheat. No light is flashing on the MFD? And your fuel level is reading correctly? Often the fuel float is the problem. Even though you have a full tank, it will read low and trip limp mode.

  8. #8
    Thanks, I will check it. The MFD does flash 7 times, don't know if that means something. The fuel float always shows full, it is stuck at the top, but maybe too high. The overtemp sensor is open circuit, so that is OK. I will put mu attention on the fuel float and give feedback. Thanks for the reply !

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Location
    Cleveland OH
    Posts
    17,330
    +1
    31
    The flashes are normal at start up. If the float reads full, not overheating, and your oil level is full I'm not sure why you're in limp mode. Have you tried testing the coil? Cut back the plug wire a 1/4" and resecured the plug boot? Tried a new sparkplug? Reason I ask is the limp mode doesn't "cut" a cylinder out, but limits the RPM.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Polaris 780 Fuji No Fire on PTO Cylinder
    By BlueFishCrisis in forum Polaris Open Discussion
    Replies: 3
    Last Post: 09-18-2014, 10:28 AM
  2. 98 zxi 1100 not firing on pto cylinder
    By ut1volsman in forum Kawasaki PWC Performance (2-stroke)
    Replies: 1
    Last Post: 02-03-2010, 05:35 PM
  3. 96 sl-780 Missing on pto cylinder at high rpm
    By gvnitup in forum Polaris Open Discussion
    Replies: 8
    Last Post: 08-25-2009, 10:26 PM
  4. Asking for help SL 780 1996
    By keywest in forum Polaris Open Discussion
    Replies: 4
    Last Post: 07-16-2009, 10:38 PM
  5. sl 780 jugs on a sl 750 will they fit??
    By slpolaris in forum Polaris Open Discussion
    Replies: 4
    Last Post: 06-19-2007, 12:28 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •