496HO loss of RPM
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496HO loss of RPM

  1. #1
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    Default 496HO loss of RPM

    Somehow I have lost about 300-400RPM on my 496HO, I was able to run up to 5,100RPM early in the season and now I am only able too turn 4700. Everything seems to be fine, just loss of RPM. Any thoughts are appreciated.

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  3. #2
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    Quote Originally Posted by BRVRBND View Post
    Somehow I have lost about 300-400RPM on my 496HO, I was able to run up to 5,100RPM early in the season and now I am only able too turn 4700. Everything seems to be fine, just loss of RPM. Any thoughts are appreciated.
    i'm gonna go out on a limb...if this is a jet boat?...the impeller could be slipping! due to the wear ring being worn out...IMO, a good place to start checking...it has to be tight with a certain amount of clearance to make thrust...just my .02 cents

    FastRat

  4. #3
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    496 HO probably means it's a Mercruiser. There are so many things that can cause that. Make sure the trim is still adjusted properly so you are getting the same trim angle as you were. Also, if it turned 5100 in May or June, and the last time it was 115 with high humidity, you can easily loose 300 rpms. And then if you have one more person or more fuel etc.....
    Of course I am going off you saying that everything SEEMS OK. Check the obvious, fuel filter for water, all plug wires on tight at the coils and plugs, etc....
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    Quote Originally Posted by FastRat View Post
    i'm gonna go out on a limb...if this is a jet boat?...the impeller could be slipping! due to the wear ring being worn out...IMO, a good place to start checking...it has to be tight with a certain amount of clearance to make thrust...just my .02 cents

    FastRat
    i think it would rev more if wear ring was worn over rev
    dom

  7. #5
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    Default HO

    Thanx for the input, I should have put more info out, it is a Mercruiser in a 25' Nordic Scandia(no hull steps) with a Bravo 1 outdrive. The trim angle is the same, I have gone up and down to max out at 4700. I have thought of the high heat high humididty, I can't test that until October trip, I hope I get my RPM's back then. Thought of maybe water in fuel, can't get the filter off and did'nt want to mess up and ruin trip. I fill up at the Luvs at the AZ 95 cut off not on the water, I did put 10 gal in at the Havasu Marina in July. So here I am, I will get the fuel filter off next trip and should have cooler air for a good test.

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