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  1. #1
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    Optimax surging at idle

    Hello Don and everyone else. I have a '07 Optimax 150 1B506951 withe the following mods:

    Simon Motorsports ECU tune and lighted flywheel
    CCMS Sport Reeds

    The problem I'm having is the motor wants surge at idle about 50-100 RPMs when running on the hose. It doesn't seem to do it when actually in the water. The issue started after installing the tune and flywheel. The motor idled fine on the hose with just the reeds. I talked to Eric Simon about it and he said it could be the reeds and that he doesn't change any parameters on the lower RPM range of the tune. He even took a second look at it. Any ideas? The motor runs perfect other than this. Should I even worry about it?

    The plugs have about 25 hours on them and the fuel system is new from the fuel tank to the VST.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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    #2
    Its my understanding that the lightened flywheel can effect idle quality slightly. I know it can in motorcycles and cars anyway.
    Last edited by Ship; 04-01-2013 at 08:54 PM.

  4. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #3
    Verify air and fuel pressures (at idle, and 5/10/15 seconds after engine shutdown).

    Verify plugs are not fouled.

    Verify fuel quality (fresh, clean, good quality fuel).

    And yes, lightened flywheels CAN affect idle quality (though Eric's should not have any substantial affect on running quality when in the water). The flywheel's purpose is to provide rotating MASS to carry the crankshaft smoothly through the alternating forces of cylinder's compression and power strokes.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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    #4
    Don and Ship,

    Thanks for the replies. I'll check the pressure soon as I have the chance. Would being in the water vs. not make a difference? I guess it could effect back pressure on the exhaust? Mine does it mainly when not in the water.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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  6. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #5
    May indeed make some change, depending on what's causing the problem.

    Should not affect air/fuel pressure readings, however... so those would be a good starting point (as above described).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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    #6
    Dan

    If you do not have access to the appropriate fuel pressure equipment, Autozone has loaner tools that you can use for FREE. They charge a credit card for the full price of the pressure kit then credit back the entire amount when you return it. I got two in order to do both sides at the same time. It worked like a charm.

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    #7
    Thanks for the advice 06 SB, I'll definitely do that if the one my dad has doesn't go high enough.

    Don,

    I had a little time today to look at a few of the plugs and they all looked like this:

    20130402_193707_resized.jpg

    Looks to me like it's a little rich. I'm going to pick up a new set. I'm going to also get those fuel and air numbers for you in the next few days.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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  9. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #8
    Massively rich.

    Start with the fuel/air pressure tests, reading pressures at:

    -Idle
    -Under acceleration
    -5 seconds after shutdown
    -10 seconds after shutdown
    -15 seconds after shutdown


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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    #9
    Thanks Don. I'll get those numbers soon.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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    #10
    Don,
    While I'm at it I want to check the throttle plate air gap. What's the best procedure for that? The manual says to use a #68 drill bit. Is that what you would recommend?
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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  12. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #11
    Follow the service manual direction on that. I would definitely recommend attaching a "hand-chuck" or vise-grip set to the drill bit, so as to prevent it from inadvertantly falling through the throttle plate.

    Specification on throttle plate airgap is REALLY tight... you need to be within +/- .002" of the specification.


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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    #12
    Don,

    I had a little time today to check a few things. Here are the fuel/air numbers I got at idle:

    Air running 78-85
    5 sec 70
    10 sec 60
    15 sec 55

    Fuel running 88-95
    5 sec 80
    10 sec 74
    15 sec 70

    The gauge was bouncing around like crazy on both the air and fuel.

    I also checked the throttle plate air gap. According to my manual it should be at .031". My .030" wire gauge wouldn't even fit in the gap without moving the plate. So I set the gap and readjusted the cam roller clearance. It didn't really help the surging though.

    What do you think the deal with the fuel/air pressure bouncing around is?
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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    #13
    Don after doing a little more research it looks like I used the wrong gauge. Mine is not fluid filled so I guess my results are useless. I'll have to get a different gauge set.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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  15. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #14
    REALLY need fluid-filled instruments for those pressure readings (you're correct).

    Make certain that the pressures for (5/10/15 seconds after shutdown) are taken SIMULTANEOUSLY. What we're really watching for is to see which pressures leak down, and how the OTHER pressure REACTS to that leakdown (that's why it's critical both pressures be read at the same time).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
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    #15
    Don,

    I took the fuel rails and injectors off today and will be shipping them to you tomorrow. In the meantime this is what I found when I removed them:

    port middle cylinder:

    20130410_174238_resized.jpg


    Port bottom cylinder:

    20130410_174245_resized.jpg

    Everything else looked nice and clean.
    2013 Stingray 198LX, 4.3L MerCruiser MPI
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  17. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #16
    Be sure to put a note (or a cheap printout of those pictures) in with the rails/injectors.

    May have a problem with #6....


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor