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Thread: Optimax 200 SJ running rough and slow

  1. #1
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    Default Optimax 200 SJ running rough and slow

    When I put away my Sportjon with the 200 Mercury Sportjet last Fall, it was performing well. I winterized it by running fuel stabilizer, quickleen and DFI oil through the engine while idling for ten minutes as I always have. Before I put it on the water this season, I replaced the wear ring with a SS relined one from Greatland welding along with a rebuilt impeller from them. Not that that has anything to do with the engine but just including it for completeness sake. I took it out and ran it for four hours this week. Right off the bat, I noticed that the engine seemed to idle a little rough. I could notice a little more vibration. I opened the doghouse and removed the engine cover to inspect it. The compressor belt seemed to whip more than usual. Increasing the throttle would smooth the engine out somewhat at certain RPMs, but still a subtle vibration to it and continued belt whip- more pronounced at some RPMs. I can hear the compressor chirping away but maybe I'm more awaare of it with the doghouse open while it's idling. The motor revs up fine and moves up and down the river OK but my top speed is diminished at WOT- from the low 40s mph to around 33-34 mph. My fuel usage was up too. I wasn't loaded heavy (two men and a boy with fishing poles) and could plane the boat at 3900 RPMs but ran it mostly at 4200. My GPS showed about 25mph when it used to move about 29-30 mph at this RPM. I returned and changed the spark plugs. The former plugs had 75 hours on them but all looked good. The new plugs didn't make any difference when I tested it again. The engine almost seems a little unbalanced.

    Could my impeller be imbalanced? Would that cause my problems?

    What else should I check besides the spark plugs that could be making the engine rough/vibrate more at certain RPMs?

    Any other ideas?

    My boat is on its 5th season and has 151 hours on the engine. I don't have access to a Mercury mechanic. I live off the road system.

    Ideas and advice are appreciated. Thanks.

  2. #2
    Member KelvinG's Avatar
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    Do you have a service manual? I live remote also and service manuals come in very handy. Anyway here are some specs you can check.
    Fuel pressure at injectors: 89 +/- 2PSI
    Air pressure: 79 +/- 2PSI
    Low pressure fuel pump: 6-9 PSI
    Lift fuel pump: 1-10 PSI
    Fuel injector Ohm resistance: 1.8 +/-0.1 Ohm
    Direct Injector resistance 1.3 +/-0.3 Ohms

    I'm not a mechanic, but I'd start with the air compressor. I lost the belt to mine once it made a HUGE difference, (could only idle to shore).

    Best of luck,
    Kelvin

  3. #3
    Member Grayling Slayer's Avatar
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    You should always be able to run the same speed at a given rpm and boat load. A change in speed at the same rpm means that something has changed with the jet.
    "I'd rather be fishing!"

  4. #4
    Moderator stid2677's Avatar
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    I would check and recheck the fuel to make sure the filters are clean and water free, old fuel will also lose some of it's punch over time.
    I have also heard that the stock intake reeds can be problematic on the optimaxs.

    Hope you figure it out,, summers are too short to have boat trouble.

    Steve
    "I refuse to let the things I can't do stop me from doing the things I can"
    Founding Member
    http://www.residenthuntersofalaska.org/

  5. #5
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    What is your full throttle rpm now? If it turns the same rpm as last year than I would look at the jet, if the max rpm is down then look towards the motor. I second the fuel comment, fuel in western AK can sometimes leave something to be desired. Try draining the fuel system and running with fresh fuel.

  6. #6

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    Quote Originally Posted by Grayling Slayer View Post
    You should always be able to run the same speed at a given rpm and boat load. A change in speed at the same rpm means that something has changed with the jet.
    I'd second this, if your weight in the boat is the same the boat should get the same speed as previously at a given rpm. If not something is wrong with the jet or intake.

  7. #7
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    I also had some UHMW plastic on the bottom of my boat. "Had" being the key word. The section in front of the intake catastrophically debonded on my last run last Fall. It's whereabouts are unknown. I noticed a lip of some type of epoxy about 5'8" in height in front of the intake. I wonder if that could be causing water turbulence ahead of the jet? I ground it down and will test it on Sunday.

    I changed my Racor filter but not the two fuel filters on the engine itself. Is it necessary to change all three?

    I will see what type of fuel economy/performance I get after changing the plugs and smoothing off the bottom of the hull.

    Thanks for your input.

  8. #8
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    Default a real newbie with a phantom sj

    This is a great thread for guys like me to read so thanks. After my first time out of the Deshka this past week, some guys probably got a big laugh as we sat on a gravel bar up the wrong slough on the upper river. 1 &1/2 hours of learning how to use the winch I put on it (fore and aft), a looong anchor rope and the wheel/jack option I'm glad I included in the package, we were back in 6 in of water. Included atv ramps under the wheels worked great, wheels kept sinking in the gravel, need to be wider! The trip actually turned out great though cause all three of us learned a lot AND got a 30 - 35 King each further up the su and later in the evening. Keep up the tips, us newbies are the new entertainment!

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