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  1. #1

    Anybody wanna help with a fun 750 Problem

    Hey guys,
    I've been searching the forum for an answer pertaining to my problem. Couldn't find anything (yet) that was the exact problem I'm having, so I'm hoping someone can help. Here goes:

    It's a '95 slt750. Bought it with holes in 2 cylinders. Rebuilt the top end with used cylinders and pistons ( good shape ) and replaced the fuel lines with new, and the pump with a triple from zig. New gaskets when reassembling. New b7es plugs too.

    Started up today and it didn't sound right. Disconnected the plug wires one at a time while idling and found that the #3 (PTO) cylinder is not firing. all plugs are firing and compression is 1-110 2-95 3-85.

    The #3 cylinder plug is at least a little wet when I pull it out, so I have to assume it's getting some fuel. I haven't taken apart any of the carbs, but I just got the manual, so I suppose that's the next step.

    So...Any suggestions ?


  2. #2
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Quote Originally Posted by aira$$ault View Post
    Hey guys,
    I've been searching the forum for an answer pertaining to my problem. Couldn't find anything (yet) that was the exact problem I'm having, so I'm hoping someone can help. Here goes:

    It's a '95 slt750. Bought it with holes in 2 cylinders. Rebuilt the top end with used cylinders and pistons ( good shape ) and replaced the fuel lines with new, and the pump with a triple from zig. New gaskets when reassembling. New b7es plugs too. typo by chance? Try BR8ES or BPR7ES

    Started up today and it didn't sound right. Disconnected the plug wires one at a time while idling and found that the #3 (PTO) cylinder is not firing. all plugs are firing and compression is 1-110 2-95 3-85.

    The #3 cylinder plug is at least a little wet when I pull it out, so I have to assume it's getting some fuel. I haven't taken apart any of the carbs, but I just got the manual, so I suppose that's the next step.

    So...Any suggestions ?
    your #3 seems a little low on compression should be right around 120 across the board with no more than a 5% difference between them

  3. #3
    I agree, I was misled a bit on this board when buying them from someone who was parting out a ski. He said they were in good condition, but not really the case. Anyway, I would think it's got enough compression to at least fire. Engine sounds the same whether I plug in the spark plug or not.

    I had a thought: Could I flip the carbs around to see if the problem follows the carb ? Will it run with the carbs backwards ? I don't see why not.

  4. #4
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    As a test you could turn the carbs around. I also think the low compression is the problem. I think I read that you need at least 90 psi.

  5. #5
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    So you just rebuilt the motor? The low compression could be due to the rings not being seated yet, especially if you have not run it yet. My compression on my SL780 was low..about 95 when I first rebuilt it and after the rings seated, it is up to 125.

    Try pulling off the plug boot on that wire, trimming the wire about 1/4" and screwing the plug boot back on. See if it fires then. Gotta try the simple stuff first!

  6. #6
    All the cylinders are sparking, but it almost seems like there's something up with the ignition. I just started it and let it idle. Dripped a bit of premix into the PTO cylinder, which is the one that's not firing. The engine revved up a bit, and I waited for it to die down. Then I gave it a little throttle, and it revved up and was slow to return to idle, so I disconnected ALL the spark plug wired and it kept running. I had to choke it to kill it. Think it's an ignition problem ? I checked the timing, and it kinda seems like it's jumping around a few degrees.

  7. #7
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    yes the carbs can be turned and actually come turned on the 780's. sounds like you got a plugged jet or something is not right there.

  8. #8
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Quote Originally Posted by aira$$ault View Post
    Then I gave it a little throttle, and it revved up and was slow to return to idle, so I disconnected ALL the spark plug wired and it kept running. I had to choke it to kill it.
    That's glow plugging like diesel engine cause you're mad lean

  9. #9
    I like Boobs. wetwolf's Avatar
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    When you say holes in 2 cylinders, do you mean 2 pistons had holes burned thru the top?? If so, then you will prolly need to replace crank bearings in those 2 holes. If te engine keeps running with all the plug wires disconnected, then it is very lean like nut#1 said.

    100 lbs of compression is a bad running motor if you can get it started. you have 2 cylinders below that mark. I would venture a guess that its time to pull a motor.

  10. #10
    I'm out in the garage fiddleing with the carbs now. I've taken apart and cleaned the carb that was on the cylinder that wasn't firing. Apartantly you can not turn the carbs around as I thought, they won't clear the intake manifold. Anyway, the only thing I found out of the ordinary is the fact that the low speed needle was only 1/2 turn out. Does anyone know what the factory settings are for the high and low speed needles ?

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