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  1. #1

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    enginw wont rev past 3400rpm

    i have a 95 slx780 that won't rev past 3500 rpm. no its not the grey wire and its not rev limited. they were riding along on the old Mississippi and all at once it started doing this and it has me stumped. i own a couple of these and know a lot about them but here's what i got. 120 compression on all 3 cylinders. swapped out the carbs with ones from my other ski. not it. replaced the fuel pump and hooked up a fuel source directly to the pump to rule out the rest of the fuell system and thats not it. swapped out the cdi. not it. has spark and i checked out the resistance of the stator and ohms are a bit low but i don't think low enough to be a problem. like 460 ohms instead of 490, 80 instead of 90 but it seems to have good spark. reeds are perfect. i even unhooked the drive shaft. the only think i can think of could be left is a twisted crank. did a stick or something go through the prop and cause it to twist? i don't know what else would do it and i'm only guessing. any other ideas or things for me to check? i did the redneck pencil test on the crank and they are all the same height. do you think its out of index? it does act like the timing is way off when you rev it. it also starts hard but it will run and idle but it just won't rev. so what do ya think? stator or crank? i'm stumped


  2. #2
    I'm addicted to Polaris PWC ghostinstallations's Avatar
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    I think you should do a dynamic timing check and if that is not it, do a proper index test. It the grand scheme of things its easier than pulling the reeds to inspect them.

  3. #3
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    Maybe flywheel key broke? Have you tried pulling off the plug boots, clipping the wire 1/4" and putting them back on?

    You said your redneck check had them all the same height? The way it should be done is one of the pistons is brought to TDC or BDC and the other two cylinders will be at the same height, but not the same height as the one at TDC or BDC.

  4. #4

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    did the plug boots earlier and the key is good. i will have to try your method of checking the piston height and maybe indexing too. i think its the crank but i don't have any reason that i know of for it to have twisted. i have another crank on hand and am thinking about putting it in but if it isn't the crank then i wasted a lot of time so thats why i'm asking the experts for ideas.

  5. #5
    I'm addicted to Polaris PWC ghostinstallations's Avatar
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    Quote Originally Posted by eamon7 View Post
    did the plug boots earlier and the key is good. i will have to try your method of checking the piston height and maybe indexing too. i think its the crank but i don't have any reason that i know of for it to have twisted. i have another crank on hand and am thinking about putting it in but if it isn't the crank then i wasted a lot of time so thats why i'm asking the experts for ideas.


    Use the method in the book. You always want to measure down some arbitrary height from TDC because of the play at TDC. The method above will not be as accurate as the method in the book. This is important when you only have +- 2 degrees between good and bad.

  6. #6

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    well we were right. i did my own indexing by finding tdc on each cylinder using a mic. and puting a mark for each on the coupler. then i checked the marks i made and one of the marks was not 120 degrees. twisted crank. i'm wondering if it binds enough being twisted and thats another reason why it won't spin any faster than 3500. i'll bet i can see it flex when i split the crankcase and spin it.

  7. #7
    I'D RATHER SWEAT THAN SHIVER hyoctane23's Avatar
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    How far off was it?

  8. #8

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    the mag one was out a couple degrees. when i split the crankcase and spun it you could see the end of the crankshaft making an oval pattern and the bearings would actually move front to back a tiny bit so i took the crank out and wacked opposite of the jurnal on the front cast and put it back in and it was almost true. so all i did was use a mic. and had to wack the crank a couple more times in the same spot until i had no side play on the end of the crank which means it was back to being true. i will probably check the end play but i'm pretty sure i got it and its going back in tomorrow. crazy huh? i actually did this method once before on my other slx780 when i pressed it apart to replace a failed connecting rod and its been running great for the past 3 years so i'm confident its ready to go. plus i still have an extra crank if i need it. i'll let you know how it runs tomorrow night. i still have no idea why it got out of index in the first place. i'm guessing a stick or something went through the prop

  9. #9

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    oh yea i used a 2lb hammer to whack it. i set the crank on my bench and hang the part of the crank i wanted to move over the edge and hit it not real hard but solid then i would put it back in the lower half of the crankcase and spin it. each time the oval pattern got smaller and all at once it was perfectly straight. took about 6 times to get it perfect but i did it. i just felt it was better putting the same crank back in rather than a used one i got from ebay plus if i didn't try to untwist it it would be junk anyway so i had nothing to lose

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