Mercury 650 problems – is it worth an overhaul?

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Viewing 10 posts - 11 through 20 (of 40 total)

  • seakaye12

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 1117
    Topics: 108
    #78095

    Yes the primer bulb needs to firm up and stay firm. If it’s soft….then fuel is leaking somewhere. If it hasn’t already been checked; add the fuel pump to your list of things to check for fuel leaks in addition to flooding carburetors. The fuel pump diaphragm might be leaking; allowing fuel to flow into the intake port.
    I have a 1977 Mercury 850 and when I got it nearly 10 years ago the wiring was so bad that I wouldn’t dare hook a battery up to it. Ready made harnesses are most likely still available; otherwise just replace one wire at a time. Hopefully you don’t have issues with the wires running up under the flywheel to the stator and trigger. Those were bad on mine and I ended up replacing those components. In the long run it was OK because the CDI brand replacement ignition components are said to be better than the original Mercury parts. Modern electronics of course.

    Multiple carburetor engines really need to be maintained (the carbs) because if one goes lean from getting partially plugged it may not be all that noticeable but can cause lean running and melted pistons.

    If you feel it might be over-revving I would take it easy until you get a tach. They are not that expensive and would make a great addition to your instrumentation.


    mercuryspecialist


    Replies: 82
    Topics: 9
    #78112

    Sneezing and hard to start are often indicators of the carburetor low-speed mixture being adjusted too lean. I like to use a pencil to draw a small line showing where the slotted (low-speed) mixture screw head is "set", and then carefully noting the amount of turn, turn (clockwise) the mixture screw until it "seats". For a 1975 model, often, the adjustment will be approximately one and one-half turns counter-clockwise open from seated. Both the top and bottom carburetors should be adjusted the same. If the mechanic did adjust carburetors to approximately one and one-half turns open, then adjusting both carburetors one-eighth of a turn counter-clockwise can be experimented with to try on the water for improvement. The specifications call for 4800 to 5300, and I would certainly want to achieve around 5300 to 5500 when lightly loaded. As a 1975 is a battery powered CDI ignition, and the ignition components are real money, I dislike reading that the wiring is "rough, but will last a season or two". Sounds like a sure way to blow/damage the switchbox (ignition module) and/or rectifier, and offer a (small) risk of an engine fire. My first thought on the reverse lock would be a missing, damaged, or incorrectly indexed reverse lock cam.


    shoestringmariner


    Replies: 258
    Topics: 53
    #78182

    Thanks guys, I’m not sure what I think of this mechanic yet. He seemed to treat my brother well I’m the past but I got the feeling I was being brushed off when I complained that my reverse lock wasn’t working. Backyard mechanic, literally. Sometimes saving a buck isn’t the wisest move I guess


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #78183

    Don’t forget, for the reverse lock to work right….and assuming everything IS mechanically correct…..you have to raise AND LOWER the motor in FORWARD gear, not running, of course. If you lower it in neutral, there’s a very good chance the hook will just sit on TOP of the angle adjusting rod, and not lock the motor down.

    Long live American manufacturing!


    dave-bernard

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 2014
    Topics: 30
    #78187

    not a good chance BUT a FACT!


    shoestringmariner


    Replies: 258
    Topics: 53
    #78197
    quote BillW:

    Don’t forget, for the reverse lock to work right….and assuming everything IS mechanically correct…..you have to raise AND LOWER the motor in FORWARD gear, not running, of course. If you lower it in neutral, there’s a very good chance the hook will just sit on TOP of the angle adjusting rod, and not lock the motor down.

    Thanks, I followed your instructions and the pawls still won’t engage. Looks like I have to drop the lower unit and have a look.


    shoestringmariner


    Replies: 258
    Topics: 53
    #78198
    quote Seakaye12:

    Yes the primer bulb needs to firm up and stay firm. If it’s soft….then fuel is leaking somewhere. If it hasn’t already been checked; add the fuel pump to your list of things to check for fuel leaks in addition to flooding carburetors. The fuel pump diaphragm might be leaking; allowing fuel to flow into the intake port.
    I have a 1977 Mercury 850 and when I got it nearly 10 years ago the wiring was so bad that I wouldn’t dare hook a battery up to it. Ready made harnesses are most likely still available; otherwise just replace one wire at a time. Hopefully you don’t have issues with the wires running up under the flywheel to the stator and trigger. Those were bad on mine and I ended up replacing those components. In the long run it was OK because the CDI brand replacement ignition components are said to be better than the original Mercury parts. Modern electronics of course.

    Multiple carburetor engines really need to be maintained (the carbs) because if one goes lean from getting partially plugged it may not be all that noticeable but can cause lean running and melted pistons.

    If you feel it might be over-revving I would take it easy until you get a tach. They are not that expensive and would make a great addition to your instrumentation.

    Thanks for your input. I mentioned that I was planning on rewiring it over the winter. He said that I had to use the exact same gauge and length of wire had to be identical as the wiring in this system is resistance sensitive.

    As for the tach, a sticker under the hood said to make sure the tach was “quicksilver compatible”. Truth or fiction?

    Also,I was told the top and bottom carb are different sizes because one carb feeds one cyl and the larger one feeds 2 cylinders. This is the strangest thing I have ever heard.

    Lastly, do you know where I might find replacement harnesses or someone who makes them?


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #78205

    Okay. It’s also important to realize that those reverse locks do not get forced up and locked by the cam, in reverse. The idea is that the hook should move freely and be returned to up/tilt position by a spring. When you lower the engine on to the tilt adjusting pin, the reverse lock hook should just gently move right around the pin and be in a position of being hooked, in appearance. Then, when you shift into neutral or reverse, the cam on the lower shift shaft moves into a position to HOLD the hook control rod from moving. You see? The cam doesn’t PUSH the rod into a hooked position, it just HOLDS it in a hooked position. This is why they can get away with a plastic cam. When the engine is tilted up and in forward gear, you should be able to move the hook freely with your hand and it should spring back. If you can, then the problem will either be that the cam is not clocked right on the lower shift shaft….or completely missing, which happens when somebody doesn’t put it back on. However, the hooks very often get rusty and will stick.

    Long live American manufacturing!


    shoestringmariner


    Replies: 258
    Topics: 53
    #78210

    Thanks Bill (and to everybody else on the board. You’ve all been tremendously helpful). I can move the catches back and forth freely. Looking at my old lower unit I can see the cam. I’m going to drop the new lower unit tonight to take a look.

    If you don’t mind more questions; can I drop the lower unit without changing the oil? My oil pump fitting does not fit the thread size. Or once I split the housing, does it expose the oil in the gearcase to accidental contamination of water dripping from the pump tube etc.

    My manual also says to take the prop off, which I don’t understand. Is this actually necessary?
    The manual (Seloc) does not impress me much. I’ve gotten 100 times better information here than through its pages.


    seakaye12

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 1117
    Topics: 108
    #78212

    Yes you can drop the lower unit w/o draining the oil. It is all sealed to keep the oil in (and water out!)

    No need to remove the propeller that I can think of.

    I got my wiring harness from CDI Electronics. I would suggest that you first go to a site like marineengine.com and retrieve the part number for the original Mercury wiring harness. You will look up your motor by serial number. You HAVE to have the serial number. Once you have the original Mercury part number (it might be 84-60795 but verify that first) then you can contact CDI and see if they can help. Other sites like Oldmercs.com might also be a source.

    Seloc manuals are of little value; I agree.

    I use a Teleflex brand tachometer

Viewing 10 posts - 11 through 20 (of 40 total)
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