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  1. #1

    Pro 785 Jetting help

    I have a limited Pro 785 with the following mods:
    Hot seat pipe (set to hot seat specs)
    Novi 46's Hot seat sidedraft intakes, diaphrams forward
    Novi vapor sepertor
    2 Novi fuel pumps
    Custom tank pickup for dual pumps
    Hot seat heads with 1 dot (pump) domes
    Randy 11 CDI
    All stock internals

    It was a race boat. I have not yet had it run right since I bought it two years ago. It was raced a Havasu a few years ago and sheared a flywheel key. It was replaced when i bought the boat and I have since replaced the flywheel and stator because a started shim left in the front case.

    The problem: the boat will not reach max rpm and doesn't climb any rpm after 3/4 throttle. It accelerates well to 3/4 throttle then feels dead lean. It had 137.5 mains with the high speeds 3/4 turn out. I tried to back them out more since I'm running 93 pump and it WAS on a race/pump mix. I got no where backing the high speeds out. I bought some bigger jets, 145's I believe, I also bought 142.5's but I put the bigger 145's in too start. The boat seemed to come around a little but was still felt lean and the plugs showed that. I ended up melting down the first cylinder, because of my own stupidity (never try to beat your girlfriend on her good running stock 785 when yours isn't running good). The other two cylinders looked to be right on the ragged edge of running lean, they were a little lean and would have eventually melted down but nothing like number 1. I found this wierd and started checking things. The fuel pressure in the boat was good when this happened, the pop off pressures in the carbs are the same and in spec.
    My question is which jets should I try next and do you think I have another problem? I thought going from 137 to 145 would do it but I guess I was wrong. I definatly don't want to have another melt down this year.
    Any help would be greatly appreciated.
    Adam


  2. #2
    Moderator beerdart's Avatar
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    Welcome to the Hulk..

    What size are the lows?
    Are the exhaust valves working and adjusted.
    Have you cleaned the carb screens??
    Are there and leaks or bad hoses in the fuel system?

  3. #3

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    can you post some pics of the motor and carbs ,with sidedraft intakes and carbs the jetting can be different depending on which way the diaphrams are facing ,up or toward the front . how many rpm's will the motor turn ???

  4. #4
    Polarisracer166's Avatar
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    Pro 785

    I had the same setup in my limited boat. Give me a call.. I can help... 585-261-3360 Jeff

  5. #5
    To answer the questions posted:
    Low jets are 145's
    Exhaust valves are clean, working and adjusted properly
    Carb screens are clean, so are the carbs
    fuel lines were replaced just before I bought the boat and are good
    the diaphrams are facing the front of th boat
    The motor will only turn 6300rpms, which can be achieved at 3/4 throttle if you roll into the gas, if you go full throttle it still only goes 6300, it's like it hits a brick wall and you can feel it loose power, it definatly feels lean.

    Jeff, I will give you a call tonight. Thanks.
    Adam

  6. #6

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    sounds like you might have a cracked pipe ,have you pressure tested them

  7. #7
    The pipes have not been pressure tested. How do i do this and what kinda of psi should they hold for how long. I think I saw a how to on here somewhere.
    Adam

  8. #8

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    you would have to remove them and test them at 10lbs of pressure and they should hold for 15 minutes or more . because your problem sounds much more than carbs ,hows the compression .

  9. #9
    compression was good, about 145-150 on all cylinders, until the mishap with the first piston. Anyone have a spare stock piston in good shape they want to sell?
    Adam

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