650sx uneven cylinder burn (single carb)
pxctoday

» Log in

User Name:

Password:

Not a member yet?
Register Now!

» Find OEM Parts

» Jobs

» wallpapers

Page 1 of 2 12 LastLast
Results 1 to 10 of 14
  1. #1
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    650sx uneven cylinder burn (single carb)

    Pretty much rebuilt my ski two whole times replacing everything I can think of. Without going into detail, what is everyoneís first thought when they see these spark plugs? Iím not looking for tuning advise because itís impossible to tell what the engine wants at the moment. Iím looking for the reason why they are different with a single carb.

    The ski runs absolutely terrible. Brand new Ada head 35cc domes put me at 150psi in each cylinder, good coil, new crank seals... I can go on and on with specs but would like first impressions. I can respond to any questions and give more details if anyone would like.

    Attached Images Attached Images

  2. #2
    Resident Guru
    Join Date
    Apr 2005
    Location
    Texas
    Posts
    1,185

    Re: 650sx uneven cylinder burn (single carb)

    Quote Originally Posted by 440man View Post
    Pretty much rebuilt my ski two whole times replacing everything I can think of. Without going into detail, what is everyoneís first thought when they see these spark plugs? Iím not looking for tuning advise because itís impossible to tell what the engine wants at the moment. Iím looking for the reason why they are different with a single carb.

    The ski runs absolutely terrible. Brand new Ada head 35cc domes put me at 150psi in each cylinder, good coil, new crank seals... I can go on and on with specs but would like first impressions. I can respond to any questions and give more details if anyone would like.

    The wet plug is probably misfiring. Try gapping them at .022" and swap the leads front to back. See if the condition follows the plug wires. Its common for older solid core plug wires to break internally and have difficulty firing a plug.
    What exactly does the IJSBA do?

  3. #3
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    Re: 650sx uneven cylinder burn (single carb)

    It’s definitely misfiring. It starts and idles perfect. But when I ride it and I give it throttle it sounds like it’s running on one cylinder. If I give it about 3/4 throttle it clears up though. I tried swapping leads front to back. The problem stays with the cylinder and does not follow the wire. Also been through a dozen plugs with the same results (all gapped the same). Tried new exhaust manifold (thought there may have been a crack), also put in new reeds.

  4. #4
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    Re: 650sx uneven cylinder burn (single carb)

    I will say that the leak down test I performed did not go as well as I’d hoped. I pumped up the case through the pulse line to 8psi and it dropped to 7psi within a minute. I stopped the test there.

    I understand that this would explain the “lean” color on the front plug. Would this also explain the wet rear plug?

  5. #5
    PWCToday.com Is My Home Away From Home Myself's Avatar
    Join Date
    Jun 2006
    Location
    Arkansas
    Age
    45
    Posts
    6,776

    Re: 650sx uneven cylinder burn (single carb)

    Many times the pressure test will drop 1-2 psi.......but will then hold steady for the next 15 minutes. I would start by replacing the plug wires into the coil and see what the plugs look like then. It's almost impossible to troubleshoot any lean/rich issue with a misfiring engine.


    Plug wire replacement.--->http://www.pwctoday.com/showthread.php?t=393820
    Last edited by Myself; 09-07-2021 at 09:54 PM.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  6. #6
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    Re: 650sx uneven cylinder burn (single carb)

    I think i eliminated any electronic/plug wire problem. I extended the rear wire to the front and connected the front wire to the rear. The fouling did not follow the plug wire.

  7. #7
    PWCToday.com Is My Home Away From Home Myself's Avatar
    Join Date
    Jun 2006
    Location
    Arkansas
    Age
    45
    Posts
    6,776

    Re: 650sx uneven cylinder burn (single carb)

    If you're sure there are no ignition problems then I would pull the carb and use a dental mirror to inspect the reeds.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  8. #8
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    Re: 650sx uneven cylinder burn (single carb)

    Already pulled the intake once before to inspect reeds. I installed brand new boyesons. I think I’m going to look into the possibility of a twisted crank. This thing vibrates like crazy so maybe that’s a sign.

  9. #9
    PWCToday Newbie DudeWithAJet's Avatar
    Join Date
    Aug 2021
    Location
    New York
    Age
    28
    Posts
    18

    Re: 650sx uneven cylinder burn (single carb)

    Did you ever fix the problem? My ski is having the same problem and I checked everything that you said that you did.

  10. #10
    PWCToday Newbie
    Join Date
    May 2015
    Location
    SoCal
    Posts
    9

    Re: 650sx uneven cylinder burn (single carb)

    Not yet… still trying to figure it out. I think I need to check the crank next.
    Also thinking about just buying a new (used) complete engine.
    Tired of throwing money at it at the moment lol

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBadvanced CMPS v4.2.0