Thread: low rpm surge

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  1. #1
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    low rpm surge

    serial number-0t512962
    2002 225 optimax. 31 hours on new powerhead. 416 total hours
    Picked up a 2002 stratos 21xl magnum about 6 months ago with a 2002 225 optimax "my first merc" I have noticed at an idle it seems to be running a little rough at low rpms once I'm up on plain and moving you can notice anything at all runs great all the way up too 5700rpms where I'm getting 70.86 on gps with a 25p tempest. Curious if its a fuel issue seeing as in las vegas I have yet to find any ethanol free fuel. also I have been running 91 with merc quick clean every other tank with merc optimax oil. After doing some reading I am not so sure the 91 is such a great idea. Any ideas as to what could be going on.

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    #2
    Change it back to 87 octane the 91 will just carbon it up.

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    #3
    I would check/change the sparkplugs and replace the fuel filter for starters....
    I do NOT suffer from CP, Compressor Paranoia (fear that my compressor will someday fail)

    Don't take others for granted, show appreciation.
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  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #4
    +1 to both of the above comments- then see how it does.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 40 years (learn something new every day).
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    #5
    Also you should be running quikleen every tank.

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    #6
    Thank you guys will fill it up with 87 from now on and also start running quikleen every tank will update after my next few trips on the lake. also replaced the fuel filter checked plugs and they seem fine not burned or fouled at all all gaped correctly

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #7
    Make sure you're using NGK: IZFR5G, gapped at .032-.033" (ONLY). Torque plugs to 20 lbs/ft with a torque wrench.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 40 years (learn something new every day).
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    #8
    Make sure when gapping your new plugs to only use a wire gauge gapper, not the round friction slide type or feeler gauge type. To keep fuel fresh between outings, you should also be using Quickare every time you refuel. See this post - Oil, Battery, Spark Plugs, Fuel and Fuel Additive Recommendations
    _______

    Phil
    '09 Hewescraft ProV
    '09 150 Optimax

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    #9
    Well update on the engine I again checked plugs nothing strange checked gap "mechanic by trade just not on boats" I have always used wire style gap tools. fuel filters were installed with the power head both fuel pumps replaced at the same time fuel system completely gone through before. I am almost positive my underlying issue showed up today wile fishing a tournament I noticed kind of a strange sound not loud or anything but enough so that I putted into a marina that was about 450 yards from where I was fishing got to the dock noise got a bit louder shut the engine down pulled the cowling off started the engine and herd this. Almost 100% positive that is a bad air compressor. you guys tell me now what do I do going forward obviously an air compressor but do I need to do anything else wile doing this.

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    #10
    Yep, that sound almost always means bad compressor. Unfortunately, the fuel/air system should be cleaned/validated when a compressor is replaced, due to the possibility of metal particles being passed through a failing compressor. Also, the two small plastic oil filters on the lines leaving the compressor should be replaced, the compressor water strainer should be cleaned, and the oil system should be re-primed.
    David Patten
    Automotive and marine technician.

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    #11
    I am going to pull the air compressor off and take a look if I see any metal anywhere I will get the fuel system checked out but if I dont see anything could I get away with not doing the fuel system i will get everything else done I just have nobody local that can do it I haven't given don a call yet but I plan on it seems like he takes care of the guys on this forum.

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    #12
    Sure you can, but you run the risk of destroying the motor.
    I do NOT suffer from CP, Compressor Paranoia (fear that my compressor will someday fail)

    Don't take others for granted, show appreciation.
    There is no substitute for experience!

  14. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #13
    Or a very high probability of trashing EVERY Direct (air) Injector.... OR both.

    Injectors are often damaged by metallic particles... you're MUCH better off to know NOW (as compared to later... after replacing a powerhead).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 40 years (learn something new every day).
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    #14
    That's how my buddies boat sounded. Wow

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    #15

    finally had a little time to get out and yank the pump off so far this is what I have seen.

  17. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #16
    Upper seal has definitely failed- time for a replacement compressor, return oil line filters (2), and have rails/injectors/hoses cleaned (and injectors validated/serviced).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 40 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

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    #17
    Quote Originally Posted by EuropeanAM View Post
    Upper seal has definitely failed- time for a replacement compressor, return oil line filters (2), and have rails/injectors/hoses cleaned (and injectors validated/serviced).
    I actually sent you an email to integrity for a quote on getting everything checked out. Tracked a compressor down and will be speaking with you about getting the rest of the pieces parts I will be needing.