Question for the guru's???
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Question for the guru's???

  1. #1
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    Default Question for the guru's???

    My boat at wot spins from 5,000 to 5,100 when running strong. About half the time after holding the throttle down for about 8 to 10 seconds the rpms drop to about 4,700 rpms. It does not happen all the time but does happen about half the time. Any suggestions? It is an enclosed motor with a small air cleaner. The motor is a 540 with an 850 carb. Any suggestions would be appreciated. I can provide more details if needed.

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    Senior Member ICECREAMAN's Avatar
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    Man, there's a lot of potentials to look at. First thing I would look at is fuel volume, ie draining the bowls. Check float level, pressure, adequate line size, things like that. 540 can suck some juice. In my experience, if the air cleaner is to small not allowing adequate air flow it will fall on its face everytime at WOT quickly. You can space the air cleaner up or just take it off for a pass to ck if thats the problem.


    Edit: Sorry, I missed the part were this question was for the "guru's" I guess I jump the gun feel free to dis regard
    Last edited by ICECREAMAN; 11-17-2010 at 05:15 PM. Reason: Post for guru's

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    Menominee, mi UP
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    i agree, fuel supply

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    Senior Member tkriley13's Avatar
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    Put the motor in a v-drive! Just Kidding I think it would be a fuel issue,is the motor still running the same? How old is the tach?are all the electrical connections good like the ground?

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    Senior Member moneysucker's Avatar
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    it could be a fuel filter or the floats being set to o low and running out of gas. Fuel pump may ba falling down too.
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    Senior Member DuaneHTP's Avatar
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    With that kind of problem, and an inclosed engine, make sure your fuel pressure is right first and then run it with OUT the engine compartment lid and the air cleaner off and see what happens. Heat build up under an engine cover can rob a lot of HP.
    Duane HTP

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    ... Some Kind Of Monster's Avatar
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    Sounds like a fuel pressure issue to me. After running WOT for a few seconds with low fuel pressure, you are draining the carb bowls and starving the engine for fuel.

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    Thanks for the ideas I will definitely look into the fuel system and air flow.

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    Senior Member moneysucker's Avatar
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    Just throw a 250 shot of nitrous on there to compensate for the RPM Loss.
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    I have thought about the nos but with my luck it would blow the first time out. Although it would be fun!!!! Just out of curiosity how much nos would it take to gain say 5 to 10 mph. Also how hard is that on a motor.

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    Senior Member moneysucker's Avatar
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    If you were to run Nos now with a possible fuel problem now you would burn a hole in a piston for sure.
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    Senior Member BrotherWolf's Avatar
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    isnt a 850 kinda small for a 540?....what kind of intake or you running?
    With Spray there is a way!!!

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    Senior Member moneysucker's Avatar
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    Where is sleeper? I am sure he has a chart for carburation.
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  16. #14
    Senior Member speedealer's Avatar
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    Quote Originally Posted by jet boat jared View Post
    My boat at wot spins from 5,000 to 5,100 when running strong. About half the time after holding the throttle down for about 8 to 10 seconds the rpms drop to about 4,700 rpms. It does not happen all the time but does happen about half the time. Any suggestions? It is an enclosed motor with a small air cleaner. The motor is a 540 with an 850 carb. Any suggestions would be appreciated. I can provide more details if needed.
    sounds like fuel to me too.
    If your engine cover has a scoop pointing forward you might try having somebody sit in front of it at wot and see if that changes anything. made a big diffference on my cruiser, ended up turning it around just a thought

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