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  1. #1
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    Stutter at 5800 rpm

    Serial number 1B974639 2013 Optimax pro xs 250. Sorry for the long post but just trying to narrow it down.
    What is happening is the motor pulls hard to 5800 rpm and then it stutters and drops to 5600 for a half a second and then picks back up to 5800 and repeat. Under the suggestion of another forum a guy was confident that I was getting water intrusion through the head seals. I pulled the heads and inspected and didn’t find anything abnormal. Resealed the heads. Started checking fuel/air system components and found several drops of water puddled behind the tracker valve and the air side of the fuel pressure regulator. Traced it back and found the same in the head of the air compressor. Resealed it. Motor seemed fine for several trips but I don’t think I was getting the speed due to the hot weather. Now it cool and again the stutter is back and I get a strong mist of water out of the air rail. I noticed last time out that my water ram pressure is at 30psi and possibly topped out on my smartcraft gauge. I don’t recall it ever being that high before. What are the odds water is getting forced through the compressor seals? Or is there some more likely cause? What I do know is I can lift my jack plate 1/2 inch and the motor will run on past 5800 no issues. I can drop the jack plate back down the 1/2 inch and instantly the stutter starts up again. When it was running right I could run 76-77 mph with a 25 trophy plus at 5950-6000. Thanks in advance for your help. Side note is a 24 pitch prop does not stutter but I only reach 71-72 at 6100. Seems more speed related.

  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2
    You're going to find condensation in the air side of the rails. For the same reasons that you have condensation in a garage-type air compressor, tank and lines. Compressing air condenses the moisture in the air you're compressing... resulting in water, or water vapor.

    Before getting too deep, let's make sure the info we have is dead-on:

    -RPM figures from SMARTCRAFT or from an Analog Tach?

    -Water Pressure gauge: Does it ZERO when the engine is OFF?

    -What Boat? Jackplate?

    -WHAT 24 Pitch Prop did you have on it, and why did you remove it?


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    #3
    Rpm from smartcraft gauge. The water pressure does zero. It is also smartcraft. BassCat Puma Atlas hydraulic 8” plate. The 24 pitch is a trophy plus as well. It is a summer/heavy load prop for me. It turns over 6k in the cooler weather. When the engine stutters I can feel the bow fall and it’ll drop about 2-4 mph on gps speed.

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    #4
    wpsi sure sounds high , when you look at tell tale does it seem extra strong at idle compared to other optis , what is wpsi other other PUMERS 6000 76-77 MPH
    .................................................. ...the scariest thing in life is the unknown ...................................

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    #5
    Pees normal to my knowledge. Gauge reads 2-3 psi at idle. Couldn’t give you a comparison to another Cat at this time.

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    #6
    One other think to note as well is I have checked fuel and air pressure at speed and when the motor acts up there is no fluctuations in the fuel and air pressure. 94 psi of air pressure and 109 fuel pressure.

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    #7
    Possibly related but found today that one of my fuel pumps took a dump today while on the muffs at the house. Looks like it may be end of the week before the pumps show.

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    Which pump? Still dead after pumping primer bulb firm?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #9
    I’m not sure. I have both high and low pressure pumps coming. It was idling and the I heard one of the pumps start screaming and then the motor shut down. It wasn’t a sound like the VST ran out of fuel but like a metal on metal type of scream. I didn’t check the bulb. I checked it the next day and it started with out pumping the bulb but the pumps sounded kinda normal but completely normal.

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #10
    Just keep in mind that if there is no fuel present (in the VST rear chamber), the pumps will squeal and grind because they are not being lubricated (fuel is the lubricant).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #11
    Ah I see what you’re saying. I did check and the VST was not empty.

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    #12
    Finally had a chance to get the boat out after installing new pumps. The stutter is still there. Not sure if this helps but I have replaced the exhaust adapter plate last fall.

  13. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #13
    When did this begin (in relationship to adapter plate)?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #14
    It ran fine for 2-3 months. After that it would do it once or twice on the first run then no issues. It was until a couple months ago that it got more dramatic when it acts up and does it all day. Would this symptom be consistent with a base or tuner gasket leak? I did replace both when put the adapter plate in. I’m trying to think of anything cause I’m baffled.

  15. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #15
    I would drop the gearcase and check carefully for signs of water in the exhaust "bells" of the tuner (or any gasket material sticking out into those passages).

    Also inspect your plug wires VERY carefully for any nicks, abrasions, or ends that do not "snap" securely onto the spark plug.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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    #16
    Pulled the gear case and I didn’t see anything to me that says water or gasket out of place. I’ll inspect it better with a bore scope tomorrow. I fed water up the tube from the water pump with a garden hose. Only place I got water was from in the tuner was between the exhaust runners. I’ve never heard them called bells if we are talking about the same thing, I learn something new all the time. Circled in the picture is the only place I was getting the water out of the tuner. I think that’s normal but please correct me if I’m wrong. I have replace the plug wires due to a split boot but the stutter was there before and after the plug wires.
    IMG_0468.jpg
    Last edited by BASSCATJUNKY; 10-21-2021 at 06:21 PM. Reason: Missed an answer to a question

  17. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #17
    Water SHOULD be present at the small opening between the two bells (exhaust ports) as that's what cools the tuner and portions of the exhaust.

    Backing up a bit- what OCTANE fuel are you running?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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    #18
    87 octane. I normally try to get it from high traffic stations.

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    #19
    I haven’t messed with it but do you think it’s possible with the fuel pump failure it’s put trash in the fuel side of the rails? Maybe restricting fuel flow?

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    #20
    Ok my mind is blown. I borrowed a 26 pitch fury 3 and it never stuttered once. I played with the engine height and trim in several settings. Boat ran 77.3 at 5980. This fury has been blueprinted and runs about the same speed and rpm as my trophy plus used to. I pulled the blowout ring of the trophy plus and will try it again as soon as I can. I’ve seen some pretty dumb things in my time in mechanics but this one tops the cake. It doesn’t surprise me prop causing top end performance issues, but it seems strange to get worse over an extended period of time.

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