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  1. #1

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    Need so HELP! High Rev

    Ok first of all thank you to the guys who have helped me up to this point!... Here is my problem that I still can not figure out! I start the motor up, if its sat for a while it will idle for 2-5sec then TAKE off and rev out the roof(not just 1/2throttle its FULL), so i shut it down asap! I have been told an air leak is the problem most likely so iv done an block air leak test and here are my findings (seem to be ok)...I put 10in vac on and after 10min, 2in lost( after 15min, 3in vac lost (7), all the way down it lost about 1in vac after 5min... so seems to check out ok? i looked for the minute leak and turned up nothing. I have always had a wonder if it possibly could be in the carbs, the scoop was it had ran great last summer, it sat for about 3 weeks and i went to start it up to winterize it and boom! my nightmare began! I now have the engine and essential electrical out so i can still start the motor out of thr ski for easy diagnosis . Is there anything that may suck the diaphrams in make them go full throttle or something, that is my only thought? thank you guys and I pray that I get a suggestion that may help find this problem!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Pulse line is hooked up correctly to the fuel pump?

    When you vacuum tested the engine, was the water jacket open to the atmosphere?

    Carb throttle shaft is spring loaded against idle screw?


  3. #3

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    first I forgot to add this is a 1995 Sl750 fyi ..... ok i sealed the pulse line and gravity fed the gas to emliminated the chance of it being a fuel pump issue no change, as far i understand your question, the throttle is closed and moves freely as it should if thats what you mean and im not sure what a water jacket is?

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by jared4brack View Post
    first I forgot to add this is a 1995 Sl750 fyi ..... ok i sealed the pulse line and gravity fed the gas to eliminate the chance of it being a fuel pump issue no change, as far i understand your question, the throttle is closed and moves freely as it should if that's what you mean and im not sure what a water jacket is?
    I was asking whether the throttle was opening itself up when the engine starts sucking air through.

    Normally there is a small spring that keeps the throttle plates closed until you squeeze the throttle lever, and then the spring pulls the throttle closed again when you release the throttle lever.

    If the spring is absent, then the throttle plates can vibrate open, which will cause the engine to accelerate.

    The water jacket is where the cooling water flows through and around the engine cylinders and heads. If any of the gaskets that seals the water from the engine internals is breached, it could be drawing air from the cooling jacket spaces, which have air in them since you are running the engine out of the water.

  5. #5

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    ok understood.... the springs are there they are staying shut, as far as the water jackets I had the exhaust pipe off (not the manifold) making that jacket area open making it if there was a leak in them it would have shown up on the leak test correct?(even if it were in one of the cyclinder areas?)

    i dont know why it has taken me this long to think of this but I am now shutting the choke blades to calm the motor down (making most likley a leak sommmewhere), now that i figured this out how to calm this puppy down i can run it for a longer period of time(with water running through) and do the starting fluid test to check for a rev change....

    now quick question if im correct I hook up the hose to the port across from the temp sensor, but will this not just run out the port beside it where the thermostat housing isvgiving unefficient cooling (should i block this off) or will it still running through all the cyclinders and exhaust cooling everything efficiently with that and the exhaust port open?

    thank you again k447 very much appreciated, people on here are awesome! you all have been HUGE help and give me hope with fixing this nightmare!

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    If you are using the reverse flush connection to cool the engine, you need to clamp off the thermostat exit, unless both the thermostat and by-pass plunger are installed. Otherwise, most of the water just dumps out through the thermostat housing.

    In fact, just clamp the exit hose off anyway, even if the thermostat stuff is all there.

    Even with the thermostat blocked, the reverse flushing water flow tends to cool the cylinders unevenly, and the MAG cylinder often gets very little cooling.

    The better way to cool the engine is to connect the garden hose to the normal cooling water inlet hose. This is the 3/4" hose that feeds from down low on the jet pump base, on the right side of the pump tunnel (when looking forward from the rear).

    This forces water to flow in the normal path through the engine.

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Gravity feeding the carbs isn't the same. The fuel pump actually supplies up to 4-5 psi at WOT or 1-2 psi at idle.

    Leak down test is acceptable.

    My guess is a clogged fuel filter or jet.

    Maybe an air leak into the fuel hoses.

    Make sure the throttle plates are synchronized and closed properly.

    Is the choke open or closed? Does it help by applying the choke?

  8. #8

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    ok i was only doing the gravity feed to eliminate any possibility that its the pulse line/fuel pump but nothing changed so I will hook the fuel pump back up. All the throttle blades are aligned correct and work properly.

    Im guess you mean the fuel filters inside the carbs, I have gone through they are all clean. Mabe an air leak through the fuel lines on the back of the carbs where there fuel inlet is, would sealing the lines and putting a vac on them prove anything?

    As far as the choke, yes thats how I am able to slow the engine down, closing the choke blades to about 3/4 shut mabe a little more.
    Just to make sure i just went out started it this morning, I had the throttle blades almost completely closed(after it was started) and it still was still around a little higher than idle speed, its gotta have a leak somewhere!

  9. #9

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    any idea where an air leak would be but not show up on my test?

    im gona try to do the starter fluid test on it in hope to find that change in rpm... gotta go get some starter fluid nd hose so i can run the water out of the garage! do I have to shut the water off prior to the engine or just sometime soon after? owill it hurt if i just let it continually run through even if the engines off for a min or 2?

  10. #10
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Check the fuel lines are not cracked or kinked.

    Check the clamps are tight.

    Try the starter fluid trick to locate the leak.

    Yes, the engine needs to be started before the water, and the water is shut off before the engine.

    You may fill the engine with water if left running.

    Make sure your throttle cable has a little slack on it, so it doesn't open the throttle if you turn the handlebars.

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