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  1. #1

    Join Date
    Nov 2006
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    slx 780 having trouble

    hey yall i have a question....or looking for suggestions....sorry so long

    i am working on a slx 780 for a friend. the first thing that i did not knowing what i had was get it running and take it to the lake. it fires up and runs fine, but when you go to give it gas it boggs out no accel at all. it seemed like a classic fuel delivery issue so i pulled the carbs and tore them apart. when i removed all the diaphrams the carbs were full of oil so i figured there must be plugged jets. they were full of oil but that is all, so i cleaned all the carbs and put them back in the ski. before i did all this i also pulled the plugs and looked inside the cyls, and they too were extremely oily. after reinstalling the carbs i hooked up a water hose and ran it and it idles fine, but bogges out with much more than a little power applied. pulled the plugs again and still wet. also did a compression test and found 120 mag 80 center 120 pto. i know the center is extremely low, but that doesn't explain all the oil in all cyls. i bypassed the shutoff and ran a hose directly from the tank to the pump and also pulled the return line. during idle and gasing it there is fuel return to the tank.

    i think there is sufficient fuel flow. could all of this be a result of that center cylinder? any ideas or suggestions guys?


  2. #2
    ph2ocraft's Avatar
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    I know I'm going to sound like a broken record but how were the filters in the carbs?

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Did someone mess with the oil pump rod? If installed incorrectly, it will run full feed to prevent engines from seizing as a fail safe.

  4. #4

    Join Date
    Nov 2006
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    the filters were clean. xlnt i think you are close to the right track. i put a little thought into this and decided to cut off all oil and run in with straight fuel and it ran for over thirty minutes and was still pumping out a lot of smoke when it finally ran out of gas and about every five minutes i would pull the plugs and check the pistons and clean the plugs. i think the crank case was full of oil as well. a couple of times after cleaning the plugs the engine would hit the sweet spot around 6300. otherwise it would run at about 4350. i think what i am going to do is keep the oil blocked off and run pre-mix to see if it is the pump.

    question: will it damage the oil pump if i crimp the oil feed line at the tank outlet?

  5. #5

    Join Date
    Nov 2006
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    colorado
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    any ideas

    i ran about 3 gallons of fuel thru the ski with the oil lines blocked off and still smoking like a siv. i put a little premix in it and tried for amother few minutes and figured that was enough. i just got the motor pulled out and i am going to try tipping it over to see if there is oil in the crank case, just thought i would see if anyone had any bright ideas on what else could be going on. i figure while i have it out i will make an injection block off plate. and fix the center cyl which has only 80 lbs. ?? is it possible that this is the problem with the others at 112

  6. #6

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    Nov 2006
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    colorado
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    tipped engine over had a little fuel/oil mix coming out but not much.

  7. #7

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    Nov 2006
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    colorado
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    gee guys i wonder if this could be the problem? i am surprised it had 80 psi on it. ine ring is embedded in the groove. i hope i can clean the cyl up. it doesn't appear to be too bad, i guess when i said that the center cyl shouldn't be the problem i was wrong but at least i am on the right track now.
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  8. #8
    Wankel till I die!! jonjonwells's Avatar
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    Good lord, You are a lucky man. You should probably get the jug at least honed if the cylinder damage isn't too bad. Possibly rebored. Good news is, you will have one pretty head soon.

  9. #9

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    Quote Originally Posted by jonjonwells View Post
    Good lord, You are a lucky man. You should probably get the jug at least honed if the cylinder damage isn't too bad. Possibly rebored. Good news is, you will have one pretty head soon.

    i do agree. the std bore on the slx 780 is 71.3 i am at 71.31 ish i don't know how far it is safe to hone i don't want to go over size because it is 71.8 and then i will be doing two good cyls. as well. what do you guys think about the damage? it is so close to out i think i could run it. the ding near the ex. port is the worst, if it would have been on the other side of the piston i would have had a golf ball head.
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  10. #10

    ?

    it is a good thing to do a complete top end kit! You will have to bore cause cylinder got hot and probably made out of round. Plus he is garunteed equal compression in all cylinders which is very good for the motor. having one piston beat down on the middle and 2 not very hard will cause crank problems! very very expensive. Just alitttle thing to think about.

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