Evinrude 25hp Big Twin Model 25018 “The Evil One”

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  • Shamus


    Replies: 35
    Topics: 4
    #245570

    Hello all,
    I bought a 1955 Big Twin 25 hp to match an electric start with the ’54 Dunphy Dolphin I am “restoring.” I have parts lists for Models 25920 and 25921 but not for the 25018, which I have learned from this forum and another one was beset by the lower seal issue. In my pursuit of setting this motor up for electric start, I have seen wiring harness diagrams for the later models, which refer to a mercury switch and choke solenoid, as well as a choke switch. Looking at the motor without pulling off parts yet, I can’t see any provision for a mercury switch (but I suppose I can add one) and a choke solenoid. The only wiring I can see are the two heavy duty cables leading from the starter motor to the boat. The boat itself was a “deluxe” model set up for a 6 volt dry cell battery wired to a key switch and a push button starter, but no solenoid that I can see, but also had two heavy duty cables that were just dangling and not connected to anything but terminated in the stern of the boat.

    Interestingly, the motor I bought has the extended gear case, which I would like to remove (because of the weight issue) but will require me to find a standard drive shaft.

    So a couple of questions:
    Does anyone have the parts list for the 25018 – is it at all different from the 25920/25921? (I looked on the inner sanctum but no 25018 parts list that I can see)
    Does a wiring diagram for the 25018 include wiring for a choke solenoid and a choke switch?
    I

    Thanks for any responses.


    frankr

    US Member - 1 Year
    Replies: 6136
    Topics: 49
    #245571

    I believe 25018 and 20519 are manual start, short and long shaft. 25820 and 25921 are electric start, short and long shaft

    25018 – 19 would not have a wiring diagram, since there is no electric start on those.

    All are beset by the seal issue. Serial number is needed to determine which seal it has.

    1 user thanked author for this post.

    trex014

    US Member - 2 Years
    Replies: 52
    Topics: 39
    #245572

    As Frank said, no wiring diagram except in the parts manuals for electric start motors.

    There should be a choke solenoid which mounts on the bottom of the carburetor bowl for that motor. Manual start motors did not have the correct carburetor bowl for the choke solenoid.

    The choke solenoids and electric starters both started as 6v accessories, but I believe around 58 or 59 they went to 12v. 6v starters are fine with a 12v battery… 6v choke solenoids WILL fry with a 12v battery.

    So use a 12v choke solenoid or 6v with the correct resistor in the wiring.

    The only switch for the choke is on the dash which for that motor would have been a push button.

    You said that motor has a long shaft gear case, and you want to remove it for weight issues… the long shaft kit weighs only 5lbs and the transom height of the boat is what will decide if you need a long or short shaft motor. 15″ for short shaft, 20″ for long shaft. Neither will perform right with the wrong length motor leg.

    1 user thanked author for this post.

    trex014

    US Member - 2 Years
    Replies: 52
    Topics: 39
    #245573

    Also, I believe to change that motors lower crankshaft seal from an oil slip seal to the better carbon seal, I think you have to split the block open and change a bearing to use the carbon seal.

    I could be wrong but I remember that for some reason.

    1 user thanked author for this post.

    Shamus


    Replies: 35
    Topics: 4
    #245583

    There’s no doubt about the serial number and the fact the motor has electric start, see photos below. The serial number is 25018-10558, which puts it squarely in the defective gear seal category. It seems to have the proper clamshell cowling for an Aquasonic. I guess it’s possible that this is a “Frankenstein” motor, cobbled from parts, but I don’t see any obvious indications of that, but what do I know? (Nothing). There’s definitely no choke solenoid on the bottom of the carburetor, but I can’t get a photo of it unless I tear it down.

    IMG_6211

    IMG_6201

    IMG_6208

    • This reply was modified 8 months, 3 weeks ago by Mumbles.

    outboardnut

    US Member - 2 Years
    Replies: 860
    Topics: 374
    #245587

    The Johnson 1955 25 hp RDE-17 (electric start) came with a mercury switch
    The Johnson 1955 25 hp RD-17 (manual start ) did not come with mercury switch
    So far all the RD-17,s I have worked on – I split the block to install a carbon seal
    I do not know what resistor to use to turn a 6 volt choke solenoid into a 12 volt choke solenoid
    I will be out of town till Sept 5th
    If you would like to talk on phone when I come back-look me up in the directory
    Everything I have learned about these 25 hp s . I learned from these message boards-thank you Frank
    Al Klebek

    1 user thanked author for this post.

    trex014

    US Member - 2 Years
    Replies: 52
    Topics: 39
    #245588

    That motor shows signs of being seriously overheated at some point in its life. The whole powerhead should be the nice Evinrude blue but the head looks brown which is a result of overheating.

    Check compression and shine a light into the spark plug holes to look for any internal damage.

    Check the powerhead just behind the back screw for the recoil assembly, theres a little silver plug that has serial and model number stamped into it, if that matches the ID tag then your motor is not Frankensteined.


    frankr

    US Member - 1 Year
    Replies: 6136
    Topics: 49
    #245589

    Manual start and electric start motors look the same except for the presence of starter, choke, mercury switch, wires, etc on the electrics. And of course the decals.

    1 user thanked author for this post.

    Shamus


    Replies: 35
    Topics: 4
    #245590

    Thanks for that info. That little silver plug has the same serial number. The compression check done by the seller showed about 100 on each cylinder, if I recall. When did Aquasonics start being available with electric? So I still have the same problem – This model (25018) is not supposed to have electric start but it does.

    compression-1

    compression-2

    • This reply was modified 8 months, 3 weeks ago by Shamus.
    • This reply was modified 8 months, 3 weeks ago by Mumbles.

    dave-bernard

    US Member - 2 Years
    Replies: 1773
    Topics: 27
    #245597

    stuck reed valves ????????


    frankr

    US Member - 1 Year
    Replies: 6136
    Topics: 49
    #245598

    So I still have the same problem – This model (25018) is not supposed to have electric start but it does.

    This reply was modified 51 minutes ago by Shamus.

    Obviously somebody added the starter to a 25018 manual-start motor


    Shamus


    Replies: 35
    Topics: 4
    #245643

    Thanks for your info, FrankR. Since you mentioned the mercury switch which was also a throttle control, apparently this 25018 does not have one. It seems like a good idea to install one. Are they available in either the old mercury style or in a new form? Since this unusual 25018 has the electric start, and I’m going to wire it to the boat, could I not use the wiring diagram you provided (thank you) and wire it in, and ignore the leads for the choke solenoid and choke switch? Thanks for your patience.


    frankr

    US Member - 1 Year
    Replies: 6136
    Topics: 49
    #245645

    The sole purpose of the mercury switch (on 1955 models) was to prevent operation of the electric starter at high throttle settings. Consider this possible scenario:.. You are cruising along at full throttle, and suddenly the motor quits because you ran out of gas. After a brief panic, you realize it is out of gas and connect your second gas tank, pump it up, and hit the starter button. The boat takes off at full throttle and maybe runs over something or somebody—or worse, tosses you out of the boat. Why??? Because when it ran out of gas and quit running, you didn’t think to retard the throttle and shift into neutral. So you started it in forward gear and full throttle. The mercury switch prevents that by disabling the starter till you retard the throttle (but it will still start in gear–at slow throttle setting)

    As for the choke and associated wires, of course you can eliminate that—you will just have to use the manual choke knob to cold-start it.

    1 user thanked author for this post.

    Shamus


    Replies: 35
    Topics: 4
    #245657

    The sole purpose of the mercury switch (on 1955 models) was to prevent operation of the electric starter at high throttle settings. Consider this possible scenario:.. You are cruising along at full throttle, and suddenly the motor quits because you ran out of gas. After a brief panic, you realize it is out of gas and connect your second gas tank, pump it up, and hit the starter button. The boat takes off at full throttle and maybe runs over something or somebody—or worse, tosses you out of the boat. Why??? Because when it ran out of gas and quit running, you didn’t think to retard the throttle and shift into neutral. So you started it in forward gear and full throttle. The mercury switch prevents that by disabling the starter till you retard the throttle (but it will still start in gear–at slow throttle setting)

    As for the choke and associated wires, of course you can eliminate that—you will just have to use the manual choke knob to cold-start it.

    So are these switches still available? I’d like to install one.


    frankr

    US Member - 1 Year
    Replies: 6136
    Topics: 49
    #245681

    Part number 376323.. They are out there, wherever you find them.

    P.S. If you install one, be sure your wiring is correct. They can be destroyed in a flash if too much voltage is applied.

    • This reply was modified 8 months, 3 weeks ago by frankr.
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