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  1. #1
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    Unhappy LOW TOP SPEED RPM`S 225 efi

    22 ft Kenner bayboat with a 2001 Mercury 3.0 225 efi with 4 butter flys (boat is only rated for a 200 hp engine) it has never turned over 5000 rpm`s since I purchased boat used a few years ago. It comes out of the hole great and runs perfert to 5000 rps but no higher even with the motor trimmed out. I have now just install chris carson reeds, block stuffers , had chris carson clean and check injectors, dropped down from a four blade 20 pitch to a three blade 19 pitch prop. New fuel filters, new QL77CC plugs, stator and added 300 ecu fuel and 300 ignition modules. Boat still runs the same 5000 max rpm as before the changes. (Engine should turn 6000 plus rpm now due to actually running a under size prop pitch size) HELP !!!!!!

  2. #2
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    Is the speed of the boat different with the two props or is it just that the 19 pitch has less slippage?

  3. #3
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    Speed is a little slower with the 19 pitch my main issue is I cannot get the engine to turn over 5000 rpm`s no matter what I do. With a 19 pitch I should turn over 6000 rpm`s. Just makes no sence.

  4. #4
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    How much hp do you think the motor has?
    How much does your boat weigh loaded?
    How fast are you with both props?
    How fast do you think that you should be going and at what rpm?

  5. #5
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    Compression test? Leak down test?

  6. #6
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    If butterfly open up all the way, look at fuel pressure at WOT and new fuel filters. Injector voltage tests from ECU? Timing? Exhaust restriction?

  7. #7
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    How much hp do you think the motor has? I would have to guess the boat has a min of 250 hp with everything I have done.
    How much does your boat weigh loaded? About 2000 lbs
    How fast are you with both props?
    How fast do you think that you should be going and at what rpm? I was running about 49 mph at 4900 rpm`s with the 20 pitch 4 blade. With the just added 300 fuel and spark ecu`s , 19 pitch prop, chris carson reeds and block stuffers I only run 44 mph @ 5000 rpm`s.. Rpm`s just wont turn up. My boat is only rated for a max 200 hp engine.

  8. #8
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    Butterflys are open 100% , new filters, I had ecu`s and timing checked by marina, Chris Carson inspected and cleaned injectors The bottom unit was removed and inspected. With the previous 225 ecu`s I was running ran exactly the same. I have had this RPM issue since I bought the boat a few years ago it runs perfect from idle to 5000 rpm`s just wont turn to 5700 - 6000 as need.

  9. #9
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    Compression and leak down?

  10. #10
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    All good, From idle to 5000 rpm I can run with or outrun 99% of
    any boat I cross.

  11. #11
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    Take a good look at the trigger make sure it's advancing and not hanging up from a wire that's tied too tight and will not allow timing too advanced. Have seen this several times

  12. #12
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    I will check appreciate it.

  13. #13
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    I actually had a marna replace my stator and put a 300 efi fuel ecu and 300 ignition ecu and it still will not turn over 5000 even with a 19 pitch prop.

  14. #14
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    Basic 2 stoke power is going to be air in plus fuel then compression, spark and no leaks then air out. To get most out of it you also need max timing, proper air to fuel and no mechanical problems or gasket leaks etc.

    I don't know the compression numbers or the leak down numbers(asked numerous times) as this will limit the hp.

    Max timing at WOT? you say it has been checked? What is it ?

    Mechanical you say is all ok?

    ECU checked, but all of your issues are at WOT, not sitting on a trailer. Injector drivers in ECU good at 6000 rpm, WOT?

    Strong spark at 5000 rpm, WOT?

    Plugs burning too rich or too lean at WOT? New plugs WOT run, immediate shut down, check plugs for burn.

    Fuel pressure at WOT?

    Temp/water pressure at WOT?

    I think testing on a dyno might help.
    Last edited by Soporific; 09-03-2020 at 09:39 PM.

  15. #15
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    Try dielectric grease on the computer plugs

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