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  1. #1

    SLX 780 acting funny after top end rebuild

    I rebuilt the top end on my 96 slx 780. Bored over .5mm I took it to the boat ramp today to break in the engine. I removed the thermostat during the process as well. It has the oil injection hooked up and I premixed the gas about 50:1. I started it up and idled it for 10 mins while slightly blipping the throttle open repeatledly. Then I checked the compression and found that 1 and 2 had 120psi, and the front clylinder had 150psi. I dont know what thats about. I let it cool off and then started it up again and kept the revs moving up and down at about 50% throttle for 10 minutes. I let it cool off and this time I rode it around and kept moving the throttle up and down. Never WOT, highest maybe 70% throttle. Now heres when I noticed the problems. It responded to throttle pretty well but it seemed it was running on 2 cylinders till it picked up a bit then it caught and really took off. But it only went about 35 mph. It seemed to be limited or something. The MFD was disconnected during all of this, if that has anything to do with it.

    During top end rebuild, I cleaned the carbs, replaced wear ring and impeller. Has new fuel pump and petcock. And I bypassed the clogged water separator as well. Its getting fuel and spark. Could the plugs just be fouled? Should I worry about the 120-120-150 compression readings? Anything will help. Thanks Guys.


  2. #2
    Cliffy's Avatar
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    Did u do each cylinder or just the one

    I recently done a rebuild on mine which consisted of just the front cylinder needing a rehone and new piston

    It had 150 compression, when 2 & 3 had 135, after running the ski on the water ive now got 145, 135 & 135 so it dropped 5 after a light run in

    I'd check ur plugs and gaps on the end of the plugs

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    With the MFD disconnected, you don't know if it was in limp mode.

    Did it sound like it was hitting a rev limiter?

    Do you have a bad gas float, oil float, or is the temp sensor grounded out?

  4. #4
    I plugged the MFD it and started the motor. No red light. I went to take the carbs off and noticed I forgot to tighten the three hose clamps around the fuel lines where they attach to the carbs. Do you think it was sucking in small amounts of air? I removed the carbs and checked the hi/low settings and the reeds. Everything was ok.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    It doesn't help, but normally an air leak leads to high revving RPMs.

  6. #6
    Well today I found that number 2 cylinder wasnt firing. It had spark. I looked into it more and saw that the carb was leaking gas into the intake as I was cranking. So it was just flooding it. Im thinking thats why it would fire all of a sudden in the mid rpm range; like a good mixture for a little bit. Would that also cause it stumple in the high rpm range and limit its speed?

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    An over rich conditon would do that, yes.

    Look into new needles and seats, and then check your pop off pressure too.

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