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  1. #11
    Click avatar for tech links/info K447's Avatar
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    Also, did you remove the spark plug caps, trim the plug wires a bit, and rescrew the caps onto the plug wires?

    Sometimes the plug wire ends becomes frayed inside and do not properly contact the threaded pin in the plug cap.


  2. #12
    I’m actually having the same trouble. But yet to check timing and woodruff key.

    1993 Polaris sl 650.

    Went thru the carbs, pop off pressure is good, compression is at 130 per, good spark, went thru the electrical and everything checks out, complete fuel system upgrade and oil block off kit, the carbs are set to spec... and I’m sure I’m forgetting something.

    It starts and wants to idle, hesitates when you give it gas and kinda chugs till it dies.

    It has good reeds but sometimes I see flashes in the mag and center cylinders.

    As well occasional back fire. This site is awesome, everything I’ve done was learned off of here and YouTube. But I’d really appreciate the help. Want to get this on the water this summer. Thanks!
    Last edited by K447; 02-27-2020 at 12:44 PM.

  3. #13
    Sorry I left some stuff out lol. The plugs are the bpr8es might have a typo in there but they are the 8s for sure. Haven’t tested it in the water and idle is adjusted to 3/4-1 I think? The pop off pressure I think is suppose to be 18-22? It’s about 20 per. It has an electric fuel pump on right now. Tried a new triple and didn’t seem to be getting enough gas but then again that could be why it’s still running rough. New fuel lines everywhere and in tank with new filter and new filter inline. The previous owner put new plug wires in to the electrical box. I have videos from them the summer before last tearing it up and it’s sat since then. Ok I think that’s it I really appreciate the help guys!

  4. #14
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Kado View Post
    ... It has an electric fuel pump on right now. Tried a new triple and didnít seem to be getting enough gas...
    The Polaris factory fuel pump, in good working condition, is certainly capable of supplying the engine.

    The higher flow fuel pump from the SL780 (IIRC) provides more Ďheadroomí to maintain good fuel pressure and flow over time.

    If neither was able to work properly on your engine, something is wrong.

    An electric fuel pump should not be needed for a Polaris blue Fuji engine. The electric fuel pump may complicate efforts to diagnose and discover what is actually wrong.

  5. #15
    Quote Originally Posted by K447 View Post
    The Polaris factory fuel pump, in good working condition, is certainly capable of supplying the engine.

    The higher flow fuel pump from the SL780 (IIRC) provides more Ďheadroomí to maintain good fuel pressure and flow over time.

    If neither was able to work properly on your engine, something is wrong.

    An electric fuel pump should not be needed for a Polaris blue Fuji engine. The electric fuel pump may complicate efforts to diagnose and discover what is actually wrong.
    I got a new triple output pump and I can feel pulses on my crank pulse line. But when I disconnected the three lines to the carbs and tried to crank it with hoses in a cup no gas came out. So where should I go from here? How can I test this? And I bought the jet ski with the electric fuel pump and thatís how they were running it for a year or two. I took that all off did the upgrades and now Iím back to the elec pump! Ugh what a head ache. Is there a possibility itís my timing? Or woodruff key is sheared? Maybe a bad crank seal? Iím working into a corner here!! Lol you guys are my only help I swear Iíve watched ever video on line I could find and everything else checks out. Thank you so much for your time! Much appreciated!!!

  6. #16
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Kado View Post
    I got a new triple output pump and I can feel pulses on my crank pulse line.

    ... I disconnected the three lines to the carbs and tried to crank it with hoses in a cup no gas came out. ...
    A cranking engine will pump fuel very slowly, especially if the fuel lines are not primed or there is an air leak somewhere upstream of the fuel pump. The fuel pump creates a mild suction towards the fuel tank. Any sources of air will create air bubbles in the fuel feed.

    Check water separator, fuel selector valve, every hose connection and clamp. Any air leaks need to be eliminated.

    One way to accelerate the fuel pumping is to prime the engine with a dribble of fuel down the carb intakes, then start it. The faster RPM (versus battery cranking) should pump the fuel much faster. Can take several primes to pump fuel all the way from the tank.

    Have you checked the fuel pickup inside the fuel tank? The very early SL model years had flexible hoses inside the tank. These rot over time and must be replaced. Later years have an aluminum rigid structure for fuel pick up. Sometimes the top fittings work loose from the vertical section and create air leaks.

    In all cases, make sure you have the fuel hoses correctly connected to the correct nipples on the fuel tank top. There are TINY markings around the cap. Photos of which is which have been posted elsewhere on here.

    You have checked cylinder compression for the PTO cylinder, correct? And checked the intake reeds on PTO?
    The fuel pump needs STRONG air pulses from the engine to power the fuel pump. Low compression or damaged reeds will weaken the pulses.

    Crank seal can be checked using a leak down test. Some effort needed to get the engine rigged for a leak down test. Sealing off various openings, and rigging up a gauge and vacuum pump.

  7. #17
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Kado View Post
    ... yet to check timing and woodruff key.

    1993 Polaris sl 650.

    ...

    It starts and wants to idle, hesitates when you give it gas and kinda chugs till it dies.

    It has good reeds but sometimes I see flashes in the mag and center cylinders.

    As well occasional back fire. ...
    Seeing flashes where? Looking down the carburetors?
    There should NEVER be fire in the crankcase. Possible causes are incorrect timing (woodruff key sheared, flywheel rotated on crankshaft).

    When the engine is assembled it is critical that Loctite be used on the crank shaft taper. The woodruff key is only there to guide flywheel assembly. Once the flywheel nut is tightened on the crankshaft the Loctite and friction is what holds the flywheel at correct timing. The woodruff key is not enough.

    Another possible cause of crankcase fire is a hole in piston. Common cause was previously running the engine hard with lean fuel delivery - melts a hole right through the piston.

    Backfiring can damage the reeds. Broken reeds = bady running engine.

  8. #18
    Quote Originally Posted by K447 View Post
    Seeing flashes where? Looking down the carburetors?
    There should NEVER be fire in the crankcase. Possible causes are incorrect timing (woodruff key sheared, flywheel rotated on crankshaft).

    When the engine is assembled it is critical that Loctite be used on the crank shaft taper. The woodruff key is only there to guide flywheel assembly. Once the flywheel nut is tightened on the crankshaft the Loctite and friction is what holds the flywheel at correct timing. The woodruff key is not enough.

    Another possible cause of crankcase fire is a hole in piston. Common cause was previously running the engine hard with lean fuel delivery - melts a hole right through the piston.

    Backfiring can damage the reeds. Broken reeds = bady running engine.
    Ok interesting... I have checked the reeds in all cylinders and the pto compression is 130 same with all of them which leads me to think thereís not a hole in the piston? I think if there was a hole it wouldnít be getting compression? And yes inside the carbs down through the intake there are periodic flashes. I would put my money on the timing or wood ruff key but hereís my problem. Aside from a through plug hole crank index check which I have yet to do I have no idea about anything as far as the timing stater or fly wheel and bendix. Iím sure I have to pull the engine of course and I need a puller for the fly wheel beyond that I have no idea what Iím looking for or where to go from there. If thatís the case then Iím all for it just need the proper knowledge on how to do so. Thanks man youíve already been a huge help narrowing this down.

  9. #19
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Keith has given you many great responses. As noted, make sure your fuel system is 100% up to par first. How about a pic of your carbs as it sits now. The older ski carbs had additional plumbing on them VS. the 780 carbs. (more chances for air leak)

    Backfiring through carbs is a big problem. Your reeds may nave been good when you looked, but may be bad now.

    Chances are it is timing problem though. You can remove the black plastic timing plug over the magneto in the front of the engine. Put the MAG piston at "true" TDC and look down the timing plug hole. The flywheel should be showing "0". If it's not, you have a sheared woodruff key.

  10. #20
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    Here is a pic of the carbs as they sit. I have been thru the fuel system numerous times. I even got a new one way valve for the tank and all the lines are hooked up correctly. Man thank you guys this is all such good info! I think my next steps are to check the timing thru the hole in the top and as well check the crank index. But if it all checks out could it be a bad crank seal? I just couldnít understand how there is combustion in the crank? Anyway let me know if you have any other points Iíd really appreciate it Iím new to the PWC world and as you can see Iíve been through a lot of this ski and I seen how to do most of it off this site and you tube lol but you guys know your stuff and once again itís much appreciated!

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