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Results 1 to 12 of 12
  1. #1

    Default 2004 150 hp Optimax speed and RPM loss. TPS?

    Hello I'm new to the board. This is my 1st post so take it easy on me.

    I bought my boat new in 2004. It is a 18' Nitro bass boat with a 150 optimax on it. Within the last year or so I've noticed about a 400 rpm and 6-7 mile per hour speed loss. I'm only able to top out at about 5100 RPM now under ideal conditions. I used to get over 5500 rpm. It's not the prop. I've recently changed plugs and when I did aside from them being carboned up it didn't look like there was anything wrong with them and they all looked the same. The motor runs smooth as can be and sounds great I just seem to have lost that real top end performance.


    Could it be that my throttle position sensor is just not letting the boat reach wide open throttle? To be honest I'm not even sure how the throttle sensor and connections work.

    Any help would be appreciated.

  2. #2
    Join Date
    Nov 2009
    Location
    Posts
    76

    Default Re: 150 Optimax speed and RPM loss. TPS?

    Did this start happening after weather got hot?I lose about 250 or 300 rpms when outside temp gets in the mid 90's.And if your like me,I put more and more tackle in mine as time goes by,Which is more weight.
    Last edited by mainliner61; 06-21-2010 at 08:13 PM.

  3. #3

    Default Re: 150 Optimax speed and RPM loss. TPS?

    Quote Originally Posted by mainliner61 View Post
    Did this start happening after weather got hot?I lose about 250 or 300 rpms when outside temp gets in the mid 90's.And if your like me,I put more and more tackle in mine as time goes by,Which is more weight.
    No it's consistant no matter what temp.

  4. #4

    Default Re: 150 Optimax speed and RPM loss. TPS?

    I should add that other then changing the plugs, water impeller, and water seperation filter this year I have never done any mantainance on it. Could there be something routine that I should have done or had the dealer do that's causing my loss in performance?

  5. #5

    Default Re: 150 Optimax speed and RPM loss. TPS?

    Bump to the top!

  6. #6
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,452

    Default Re: 150 Optimax speed and RPM loss. TPS?

    If the plugs were a little carbon fouled then you could have carbon build up in the heads, piston rings etc.

    Try de-carbing the motor - easiest way to do it on this model is add Seafoam to the gas..

  7. #7

    Default Re: 150 Optimax speed and RPM loss. TPS?

    Quote Originally Posted by galamb View Post
    If the plugs were a little carbon fouled then you could have carbon build up in the heads, piston rings etc.

    Try de-carbing the motor - easiest way to do it on this model is add Seafoam to the gas..

    Well when I filled up before I brought the boat out last I did dump two 16oz cans of Seafoam in the 40 gallon tank so well see if that helps. The motor probably only has about an hour of run time on it with the seafoam. I've only run the Mercury quickclean through it once in the 5 years that I've owned it so maybe that's the case.

    Is the amount of Seafoam I added (just under 1oz per gallon) enough to decarb an engine and is it possible to add too much Seafoam or could I dump another can in? How long would it typically take to see results.

  8. #8
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,452

    Default Re: 150 Optimax speed and RPM loss. TPS?

    You need to run most of it through before it will really make a difference.

    A portable 3 or 6 gallon plastic tank with your "concoction" is often the best way to quickly get it through the system...

  9. #9

    Default Re: 150 Optimax speed and RPM loss. TPS?

    Quote Originally Posted by galamb View Post
    You need to run most of it through before it will really make a difference.

    A portable 3 or 6 gallon plastic tank with your "concoction" is often the best way to quickly get it through the system...

    Should I run more the 1oz to 1 gallon??

  10. #10
    Join Date
    May 2007
    Location
    Inverary, Ontario, Canada - The Great White North Eh!
    Posts
    8,452

    Default Re: 150 Optimax speed and RPM loss. TPS?

    I never use SeaFoam so don't know what's recommended - a little heavy wouldn't hurt however...

  11. #11

    Default Re: 150 Optimax speed and RPM loss. TPS?

    After doing some more reading it sounds like it may be possible to speed up the decarbing process by just removing the water/fule seperation filter, dumping out the gas in it, and then filling it with seafoam and running the motor at cruising speeds for about 20 minutes. Has anyone done it this way and did you have decent results?

  12. #12

    Default Re: 150 Optimax speed and RPM loss. TPS?

    The Merc Quickleen is the best. I usually tell my customers to double up on the first dose(2 oz. to 6 gallons). Run the boat1/2-1 hour, let sit overnight(soak time), run again for about an hour, usually notce a diff in this time or one more cylcle.
    Hooking motor up to the merc diagnostic system(merc dealer) can determine if throttle is open all the way.

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