Page 1 of 2 1 2 LastLast
Results 1 to 10 of 15
  1. #1

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1

    Weird Problem: Centre doesn't work - 1995 SL750

    This is a recent issue that surfaced after correcting my lean condition that melted my PTO piston on the exhaust side. There is a thread I started about it, but I'm thinking this a new problem might justify it's own.

    I'd appreciate any new ideas or opinions, because as K447 said "we're grasping at straws".

    Original repair:
    - Replaced PTO piston, pin, clips, cylinder and head along with all new head, exhaust and carb gaskets.
    - Rebuilt carbs with Mikuni kits. Pop-off close and within spec for all three.
    - Replaced petcock and all fuel lines with reinforced hose back to the tank. Original restrictor in place in return line.
    - Checked and opened the Mukuni triple-outlet fuel pump for problems. It was clean inside and the gaskets and membrane were in very good shape.

    Once I had everything back together and the fuel system primed, it started without issue... well, except for the centre cylinder ó it was significantly cooler than the other two. I removed all three plugs, connected the leads, grounded the bases and pushed the start button ó all three plugs had what looked to be good spark. I then installed just the middle plug, started it and it started/fired, roughly of course. After letting it cool I installed the MAG plug, and again it started. So now two cylinders are running. After letting it cool again I installed the PTO plug and started it. Once again only the PTO and MAG cylinders fired and the CTR stayed cool.

    So the CTR cylinder gets spark and fuel to run on it's own, or with one of the other cylinders, but apparently not all three at once.

    So far since this new problem arose, I've tried the following with no change to the problem...

    1. installed new NGK plugs correctly gapped
    2. trimmed back plug leads 1/4"
    3. tried known good battery
    4. tested by swapping the PTO and then MAG plug leads with the CTR
    5. checked resistance on stator and coils cold and after warmed up Ė all within spec
    6. tried known good CDI borrowed from a friend
    7. gone over the fuel pump pulse and fuel hoses to ensure no kinks, and reduced their length where possible.

    No matter what, the centre will only 'work' if it's only one or two of the three cylinders connected.

    I have a rebuild kit coming for my fuel pump later this week which I will do. I could also acquire and install a different magneto/stator at some point in the next week or two, but that's one job I really don't want to tackle again, unless it's my final option!

    I'm hoping some "new eyes" might see this thread and provide some other ideas I can check into, or some "old eyes" might see this in a different light, if it's in a different thread.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,574
    +1
    1,272
    Just to say you have checked it, check that the crankshaft is in phase. 120 degrees between each piston at TDC.

    It would be weird if the crank was twisted such that it would still run on each individual cylinder but not run with all three firing.

  3. #3

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    Quote Originally Posted by K447 View Post
    Just to say you have checked it, check that the crankshaft is in phase. 120 degrees between each piston at TDC.

    It would be weird if the crank was twisted such that it would still run on each individual cylinder but not run with all three firing.
    I did actually check that already after I installed the new piston and cylinder using a pretty crude system consisting of a piece of circular cardboard fastened to the drive coupler and a stiff piece of wire as an indicator attached to the fuel pump mounting bolt. I then stuck a pencil in the spark plug hole to find TDC on each piston and marked the disc at each. After doing all three I removed the disc and measured with a protractor and all were exactly 120 degrees apart... which I was surprised at considering the crudeness of my "McGyver" index wheel.

    I checked it it because I was worried that maybe the melted piston had maybe seized in the cylinder at one point and knocked it out of whack.

  4. #4

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    Okay, I've been troubleshooting this morning...

    - carb hose connected properly: check
    - block ground tight and clean: ok, no change
    - spark while running with a timing light: check
    - each pump hose delivering fuel: check (lots!)
    - try fuel switch on reserve setting: no change
    - check fuel pump pulse line for fuel fouling: clear
    - check fuel return line from carbs: nothing! Not even a drip!

    Could this somehow be causing my symptoms of the CTR and possibly PTO cylinders not firing? I might swap in a length of clear hose withou a restricter to see what I get. Hopefully this isn't in the newly rebuilt and cleaned carbs.

  5. #5

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    i removed opaque black return hose, tried a clear hose (with and without the restrictor) and fuel is now returning. There may have been a blockage in the restrictor that I cleared, or maybe I just didn't run it long enough before to have the fuel come out the end of the opaque black fuel return hose. I'm going to replace the black hose with the restrictor and test again... a bit longer this time.

  6. #6

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    Return hose not blocked and operating as expected, I think.

    I truly believe this is a fuel delivery issue at the middle carb so I removed carbs again to double check. Maybe something (dirt, bugs, etc.) was in the newly installed hose that flowed out and into my middle carb, as I was thinking it might be a blockage of the high speed circuit. It would explain (in my head anyway) why all three cylinders spark and fire, but I can't get over 4000rpm under load on the water, and the CTR cylinder stays cool.

    When I got it apart it appeared the high-speed check valve was stuck down with something white?!? I had fully rebuild these less than 6 weeks ago and have used nothing but new gas and oil premix. All I can think is it might be an errant drop of Blue Permatex and I believe I heard it goes white when exposed to gas. I cleaned this up, reinstalled the carbs and tried it out. Initially it hesitated and sputtered on the water, but once it warmed a bit and I increased the throttle it went beyond 4000rpm this time up to around 6000, so I thought I had solved it, but it sputtered about 10 seconds later and slowed once again to 4000, then about 10 seconds later shot back up to 6000 for 5 seconds, and again, back to 4000. I ran it for another 5 minutes at alternating throttle levels hoping it would settle and resolve itself, with no luck.

    So off came the carbs again to double check and more thoroughly clean all circuits on the CTR carb. I thought I was before, but this time I spent at least 45 minutes on this one carb. Nothing seemed amiss this time, so I reinstalled and tested – still the same symptom as my first post.

    Now I'm wondering: Can the PTO and CTR carbs be easily swapped by changing the throttle/choke connectors? I think if I do this I can then confirm if this problem is a carb problem or not.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    Location
    near Toronto, Canada
    Posts
    36,574
    +1
    1,272
    I commend your perseverance with this problem!

  8. #8

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    Quote Originally Posted by K447 View Post
    I commend your perseverance with this problem!
    There's a thin line between perseverance and insanity!

    I can't just chuck the whole thing — that would be wasteful!!

  9. #9
    john zigler's Avatar
    Join Date
    Aug 2006
    Location
    WI
    Posts
    2,545
    +1
    33
    How are you checking spark?

    Put spark testers on all 3 plugs, and run without the seat on, and watch under load. I am betting you are dropping a cyl spark wise......

    You need 3 of these;

    https://www.watcon.com/tools/engine-1/spark-tester

  10. #10

    Join Date
    Jun 2007
    Location
    Toronto / Grand Bend
    Posts
    129
    +1
    1
    Quote Originally Posted by john zigler View Post
    How are you checking spark?
    I last tested it out of the water with an induction timing light, but I never tried under load – would that make a difference?

    What I have a hard time wrapping my head around is that it always seems to be the CTR cylinder that isn't running. If I swap either of the working MAG or PTO spark plugs to the CTR – the CTR still doesn't work. Swap either of the good working plugs leads to the CTR – still the CTR doesn't work. After doing those two tests I can only speculate that the CTR cylinder isn't as good a ground as the other two. Is this even possible?

Page 1 of 2 1 2 LastLast

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. 1995 SL750 weird engine power loss and die
    By SeaBee63 in forum Polaris Open Discussion
    Replies: 69
    Last Post: 07-19-2014, 01:15 PM
  2. 1995 sl750 running problems!
    By Trent_sl750 in forum Polaris Tech Tips and Info
    Replies: 25
    Last Post: 07-10-2014, 05:21 PM
  3. 1995 sl750 head work
    By Trent_sl750 in forum Polaris PWC Performance
    Replies: 12
    Last Post: 02-28-2014, 10:55 PM
  4. 1995 Raider!!! Weird Problem
    By mobilesat69 in forum Yamaha Old School Skis
    Replies: 4
    Last Post: 01-11-2011, 07:05 PM
  5. a bit of a weird problem, can I have opinions please???
    By rxp_boy in forum 4-Tec Performance
    Replies: 9
    Last Post: 11-15-2005, 01:39 PM

Posting Permissions

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