Thread: LOW RPMS

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  1. #1
    Member
    Join Date
    Feb 2023
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    Lake George, NY
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    2

    LOW RPMS

    I bought a 2013 Nitro Z-7 with a Mercury Pro XS Optimax 150HP 2-stroke. I'm only getting 4900 RPMS WOT fully trimmed up. No jackplate. It has a 23P tempest 3 blade. I did swap the stock Minn Kota Maxxum 70 for a Fortrex 112. I imagine that added some weight, but other than that I can't figure out why my RPMS are so low. I should be getting close to 6000 right? Also on another note any idea the size of this gas tank? Nothing in the manual and online says anywhere from 24-40 gallons so I have no clue.

  2. Member
    Join Date
    Apr 2020
    Location
    Ontario
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    590
    #2
    Need to make sure the motor has a clean bill of health before anything else. Make sure you actually are getting full throttle, check the cable.

  3. Member
    Join Date
    Feb 2023
    Location
    Lake George, NY
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    2
    #3
    cable is set.

  4. Member
    Join Date
    Sep 2022
    Location
    Center Point, Iowa
    Posts
    90
    #4
    I have had the same issue with mine last year and the guys on this board have been alot of help. I agree with 1st make sure the motor is running correctly since it is new to you. Have a mechanic give it a tune up or buy the Factory issued Mercury service manual and do it yourself. I found my motor to be way low on the prop to pad. That gave me about 300 more RPM. And I am in the process of testing props (lower pitch will add RPMs). The guys in the prop section are pretty good at getting someone in the right direction there. If you have motor questions the guys in the Mercury motor section are very helpful. Make sure you give them the motor serial number when asking for info it helps them help you. I do know I read that if you do not get that motor into the factory RPM range WOT then you risk damaging the motor. I like learning and fiddling around with things like this but it can be frustrating. Feel free to message me if you have any questions and stick with it you will get it figured out.
    Todd Kress
    1993 150HP XRI 17 pitch worked Tempest Plus
    OD232323
    1993 Procraft 200 combo

  5. Member
    Join Date
    Jun 2004
    Location
    Ooltewah
    Posts
    521
    #5
    Quote Originally Posted by TKress View Post
    I have had the same issue with mine last year and the guys on this board have been alot of help. I agree with 1st make sure the motor is running correctly since it is new to you. Have a mechanic give it a tune up or buy the Factory issued Mercury service manual and do it yourself. I found my motor to be way low on the prop to pad. That gave me about 300 more RPM. And I am in the process of testing props (lower pitch will add RPMs). The guys in the prop section are pretty good at getting someone in the right direction there. If you have motor questions the guys in the Mercury motor section are very helpful. Make sure you give them the motor serial number when asking for info it helps them help you. I do know I read that if you do not get that motor into the factory RPM range WOT then you risk damaging the motor. I like learning and fiddling around with things like this but it can be frustrating. Feel free to message me if you have any questions and stick with it you will get it figured out.
    All this is good advice. Hopefully your engine will check out good and your low rpms are related to your engine is too low and perhaps you need to go with a 21 pitch prop. 23 on a 150 for that hull seems kinda high to me. As mentioned you for sure want to prop for the upper end of your engines WOT range, it takes rpms to make power and lugging the engine will have bad consequences.