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  1. #1

    New to the forums HELP!!

    I just picked up a 00 pro 785 that the owner rebuilt with a new crank, casings, gaskets, seals, pistons and so on. Well here is the deal. I bought it because after the owner put it together they couldnt get it running. I got it for 1500 as is. I brought it home and found out that the compression was bad.

    I took the head off and instantly found the problem.... they put the pistons in backwords!!! I checked the cylenders and they were all good so I bought a wiseco top end rebuild kit and put it in with newly honed cylenders. I put it all back together THE RIGHT WAY and it now starts but does not run very well. It will kind of sputter and backfire in a way. It has a 120-125 compression with non seated rings and just idles fine but wont rev too well.

    I think that it is the carbs that are needing to be gone through so I was wondering if this is what others think it could be and if so what are the settings for the carbs on the 00 pro 785 motors? Also if it matters I did the oil injection so do I need to retune for that? Thankls in advance for the help and look forward to meeting with the rest of you on the forums!

  2. #2
    ph2ocraft's Avatar
    Join Date
    Apr 2006
    Campbell, Ca.
    pro, WELCOME to the green Hulk Forums!!

    It certainly doesn't hurt to go through the carbs and make sure everything is clean and working well. Be sure to check your pop off and verify the needle/seat don't leak. Spend the little extra time and make sure all of the butterfly flaps are opening at the same time.
    Since you will be that far into the intake I'd pull the manifolds and check the reeds as well.

    I don't have the carb specs on your year but I'm sure somebody will.

  3. #3
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    Why do you think the pistons were in backwards?

  4. #4

    Join Date
    Aug 2006
    Homer Glen Il.
    Why do you think the pistons were in backwards?

    yes i have the same ??? please take a pic with your head removed. arrows should point toward the front Mag cylinder .

  5. #5
    Quote Originally Posted by Hydrotoys View Post
    Why do you think the pistons were in backwards?
    I have been working on motors for many years now and I know that the pistons were backwards because where the rings meet together that side of the piston is supposed to face the intake side due to there are runners on the intake port that the joint ring spot rides on. If you were to put them backwards they would be facing the exhaust port which is one large port and the rings would pop out as they entered that port causing the top of the piston to pop off and reck the new top end that the guyput into the motor.

    How do I check the pop off, does anyone have a writeup on it? Where do I get the tool or can a person make one? Is 120-125 good for compression on a fresh motor that has not set the rings yet? Does anyone have the carb specs for this machine?

  6. #6
    I bought a 750 head and piston that had the piston installed backward it actually snagged the port and caused the ring to chip! it could have been way worse! Z

  7. #7
    Does anyone have the information I need listed above 2 posts? I want to get the thing running by Friday. Thanks for the help!

  8. #8
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Search the Tech section it's all there.

  9. #9
    Never Time To Ride antoniodef's Avatar
    Join Date
    Nov 2006
    Waterford, Michigan
    Read through this thread, the guys told me how to check pop off, all the links are in the thread on how to do it.

  10. #10
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    Welcome to the forum !

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