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  1. #1
    OLDJETSKIMAN's Avatar
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    Back from ride awsome machine but problems

    Back from riding the pro today. Your right it put a smile on my face. Fired it up on the boat ramp ran great. Put it in the water started up then stalled. Took for ever to get it fired back up but then it ran great for 30min. then it shut off again, waited a few minutes it fired back up and ran great agian for 30min. I was happy pulled it out andcranked it up , ran wide open so shut it off. Got it home fired it up again to flush it and it ran wide open again, pulled the leanyard did not stop! ulled all three plug wires and it keept running until I PULLED THE CHOKE ALL THE WAY ON! I have never seen this before, it ran on comp. only! Any ideas were to start? Thanks I am telling you it blowed my mind how was this thing running with the spark plug wires disc.?


  2. #2
    Moderator beerdart's Avatar
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    Sounds like you are running lean and sticking a piston.. Time to take a look at the carbs.

  3. #3
    OLDJETSKIMAN's Avatar
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    Thumbs up

    Thanks beerdart, so lean cond. will cause it to keep running like that? I checked the comp. and still have 150 on all cyl. and it turns over great! The buddy of mine said he went thru them but somethings wrong so I will do it my self. By the book!!! I am so glad it did not do this while Iwas riding it, I would freaked out!!!

  4. #4
    Moderator beerdart's Avatar
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    It will only do it under no load condition. The spark plugs glow and keep the engine running. It could also be a air leak causing the lean condition. Time for a pressure test..

  5. #5
    bowsniper's Avatar
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    Hi all. I'm no pro on jet skis but i do know if an engine runs lean, the cylinder temps rise so high that spontaneous combustion can occur with no plugs firing. or sometimes, a lil piece of carbon is on the piston top and glows like a plug and that fires the gas mixture.
    That would be scary if i pulled the plugs and it was running wot with no plugs.lol Yikes... I guess that could be preignition or detonation depending...
    Abnormal combustion (Detonation)
    When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat, pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur. Detonation is characterized by an instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front.
    A local shockwave is created around each pocket and the cylinder pressure may rise sharply beyond its design limits. If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. The simplest deleterious effects are typically particle wear caused by moderate knocking, which may further ensue through the engine's oil system and cause wear on other parts before being trapped by the oil filter. Severe knocking can lead to catastrophic failure in the form of physical holes punched through the piston or head, either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system.
    Detonation can be prevented by the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear); decreasing the manifold pressure by reducing the throttle opening; or reducing the load on the engine. Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures at the engineering level by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation.
    Knocking is unavoidable to a greater or lesser extent in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke. There is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design. Careful design of the injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. Engines using indirect injection generally have lower levels of knock than direct injection engine, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing a more complete mixing of fuel and air.
    An unconventional engine that makes use of detonation to improve efficiency and decrease pollutants is the Bourke engine.

    [edit] Pre-ignition

    Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.
    The phenomenon is also referred to as after-run, or run-on when it causes the engine to carry on running after the ignition is shut off, or sometimes dieseling, in reference to the fact that a heated diesel engine may, by design, run without an external ignition trigger so long as a suitable fuel/air mixture is supplied to the cylinders. This effect is more readily achieved on carbureted gasoline engines, as the fuel supply to the carburetor is typically regulated by a mechanical float valve and fuel delivery can feasibly continue until fuel line pressure has been relieved, provided the fuel can be somehow drawn past the throttle plate. The occurrence is rare in modern engines with throttle-body or electronic fuel injection, as the injectors will not be permitted to continue delivering fuel after the engine is shut off, and any occurrence may indicate the presence of a leaking (failed) injector.
    Preignition and engine knock both sharply increase combustion chamber temperatures. Consequently, either effect increases the likelihood of the other effect occurring, and both can produce similar effects from the operator's perspective, such as rough engine operation or loss of performance due to operational intervention by a powertrain-management computer. For reasons like these, a person not familiarized with the distinction might describe one by the name of the other. Given proper combustion chamber design, preignition can generally be eliminated by proper spark plug selection, proper fuel/air mixture adjustment, and periodic cleaning of the combustion chambers.[citation need

  6. #6
    OLDJETSKIMAN's Avatar
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    Just got off the cell with KEZBUM said the same beerdart. said to check the intake bolts and make sure I have no air leaks said if that not the problem may be sucking air in thru the crankcase case. I have been a diesel mech. 25 yrs never new a gas motor would run like a diesel on comp. only. Any I love the machine. Got all winter to get it right. I will keep you posted on what I find. Thank you all so much!!!

  7. #7
    Your first Runaway motor is usually cause for an underwear change

  8. #8
    OLDJETSKIMAN's Avatar
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    YOU DAMN RIGHT!!!!!It is ok because I have this great forum that will get me thru this. If I need to rebuild from the hull up, so be it! This is truly one of the awsome machine of its aira! Thanks to all the great polaris guys!!!!!!!

  9. #9
    casey67's Avatar
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    An engine running hot + low octane fuel will contribute to running on.
    With 150 psi compression,I think you need at least 93 octane.
    Running race gas will help,or at least help from burning a piston before you figure out the problem.

  10. #10
    Watcon's Avatar
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    Time for a new lesson plan.

    This is the perfect time (winter) to do things right!!
    Pull the motor ,split the cases and install new OEM crankseals.. Then you can inspect everything during assembly and leak test the motor on the bench.. Most skis that are over 3 years old have some sort on minor air leak somewhere..

    Buy an OEM Polaris service manual, ($55.00 from me) and learn to rebuild it...You will have a better performing ski and you can visually inspect every part during the process.. If you can chang a stator, you can rebuild the motor.. Removing the flywheel & drive coupler are the most difficult parts..

    If you ski "free revs" on the trailer or garden hose, just pull the lanyard and hold the throttle wide open... The extra incoming fuel cools the charge and kills the pre-ignition... This is also healthier than pulling off the spark plug cap... Hahaha!~

    A few of you guys could do a "group" rebuild session, and I will offer input if needed..

    Randy

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