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Thread: Desperately need help from the 40 Merc guys

  1. #1
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    Default Desperately need help from the 40 Merc guys

    I've got a 2003 40 hp Mercury that is giving me fits. Its the 59 ci 3 cylinder 2 -stroke motor.
    I've had the reed plate worked over, the reed stops are still in place, but have been bent out it looks like. All the gaskets are good on the front end. Timing is set for maximum advance (I've played with this and haven't gotten any noticeable difference in performance). Has good even compression on all three cylinders at 140 psi exactly. And here's the kicker...it runs great with the stock 40 hp carbs.

    However, with the 60 hp carbs, the newer WME- 45 models, top speed and performance is right around 5/8th throttle. If i give it more throttle, I actually see a drop in rpms and speed not a gain like I would expect. I've ran two sets of these carbs with no change. I've went as far as to ship both sets of carbs to a friend who put them on his motor, which is exactly like mine, just 2 years newer, and they ran awesome.

    I'm running #62 jets with 87 octane fuel with an oil mix of 50:1 and Chris Carson sport reeds.

    I've been dealing with this issue for some time and don't know where to go from here. Very frustrated and need some help.

    Thanks

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    At the risk of sounding over simplistic and possibly insulting you, unless your friends motor was just EXACTLY like yours (you mention potential reed/reed stop problems, max spark advance, etc. as the condition of your engine and also a different model year) and being tested on the same type, size and wgt of boat, with the same prop, at the same set up height and kickout, it is very hard to compare carbs run on one engine with another, or any other parts run on one engine to another, especially as you mention you had to ship them to him which would also indicate a different location for the test.

    You have a lot of variables just in your short description of the problem.

    You mention his motor is 2 years newer., although you think they are the same. Have you checked the mfgr specs to be absolutely sure the motors are in fact the same?

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    Not trying to be an a**...

    Rev limiter disconected? You didn't mention it...

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    Rev limiter has been disconnected

    Bill,

    My motor and the other motor that the carbs ran great on are the exact same motors. Both 59 cubic inch 3 cylinder 40 mercurys. Both are long shaft, electric start and are on the same size (1548) boats. The reed plates were also done by the same individual. Spark plugs are the same and timing has been adjusted the same. I'm running in Southeastern Missouri and my friend is in Lake Charles, LA. Elevation differences are minute.

    The motor runs up to 6000 rpms with a 14p prop when the 40 carbs are on there...put the 60's on the motor and it will run up to around 5900, but when more throttle is applied, rpms and speed start going down.

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    "Normally" the first thing thought of when the throttle is opened from a partial opening and the motor slows down is fuel starvation, although there can be other causes such as a faulty electronic ignition if so equipped, problem with stator, etc. Are you sure you are getting plenty of fuel to and thru the carbs when installed on your engine? Have you tried pumping the bulb in the line from the tank to the carbs when it starts starving for fuel. If it picks up and goes while pumping the bulb, then you have pretty well solved the problem, at least as far as diagnosing the problem. Then you still have to fix the obstruction.

    You might check for tank vent completely open, partial fuel line/hose/filter blockage or any other type obstruction/constriction, fuel pump if crankcase vacumn operated having check valve or diapahram problems, and also as I also live in Missouri also and we have usually only ethanol based fuel sold at gas stations and that is where you get your fuel, that can cause problems also by breaking loose any deposits that may have been in the fuel system if you have just started using it or the motor is used infrequently and ethanol laced gas sits in the fuel system for long periods of time between use.

    There are lots of smart folks on this site and I am sure you will get lots of suggestions here, but another place to try is "scream and fly" which has a very good tech forum for problems like this.

    Good Luck


    Add: You might check and see if you have something blocking the inlet needle/seat assembly also. It only takes a very small piece of trash to cause a problem. I am not familiar with these carbs but a lot of carbs have a plug that can be removed in the close vicinity of the inlet needle and seat so as to remove it. Usually you can get it out with a small socket set and then "flush" the carb by pumping the bulb and letting the gas run right thru the carb into a container of some type, hopefully not around the campfire when doing this.

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    I'm not positive that it is not starving for fuel...I really never thought about that until now. I'm keeping fresh fuel (no older than a week from the pump) in at all times and always add a stabilizer. I will check my fuel delivery and make certain that is not the problem.

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    mate take the reed stops out and fit the washer style one that the 55/60hp motors run.
    when you fitted the carbs did the carby gaskest fit nice not over hanging a bit?
    do you have a pic of your reed setup?
    140 psi is good mate ,my old girl only pumps about 112psi

    i forgot to ask what jets are you running the 60 carbs?

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    i just seen reread your post .062 jets are to much mate.a stock 60 only runs .060 and most guys lean them down.
    i'm running .056 in my mine ,with a nice light coffee colour plug .i've tried .060 .058 and .056 .the .060 jets felt like a slug up top.

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    BR, take it with a grain of salt, but I'm wish FS5 on this. I think you need to go with a smaller main jet. You ought to get a set of each size down to .056 and set what happens.

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    The next size down that I have are 58's so I'll give them a try. I also removed the in-line fuel filter between the carb and the pump. Just gotta wait until monday to get back to my boat and try all of this stuff.

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