18HP saga continues. Can’t get past 14mph and 3,900 RPM.

Home Forum Ask A Member 18HP saga continues. Can’t get past 14mph and 3,900 RPM.

This topic contains 62 replies, has 14 voices, and was last updated by Avatar stephenspann27 1 year, 5 months ago.

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  • Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #8408

    **PLEASE READ ENTIRE POST BEFORE OFFERING SUGGESTIONS**
    I have a evinrude/Johnson 18hp outboard. It’s got a ’61 Johnson powerhead and the leg is from a ’65 evinrude. I bought this motor not running (it was all a 1965 model when I got it). I couldn’t ever getting it running right with the carb and powerhead it came with. I could never get the fuel float needle to seat on the original carb, despite having a new float and needle.
    I bought a carb off ebay, and finally got it running but it had a bad missfire at low RPM. I replaced the coils, points condensers and couldn’t get rid of the missfire. I finally just bought a whole other powerhead off ebay.
    The new powerhead had the same missfire. I pulled the deflector’s off the side of the ebay powerhead and found score marks on the pistons fromm overheating. Despite having decent compression around 105PSI, I couldn’t get the motor to run over 13mph. I thought maybe the rings/pistons and bores were in too bad of shape to go any faster.
    I bought, yet another powerhead of a AOMCI forum member. He said it had fresh rings in it. To my dissapointment after pulling the deflectors on that motor I found the pistons badly scored. He said that the bore was fine,and he had installed new rings. The powerhead did have good compression. WIth this now.. 3rd powerhead I still wasn’t able to get passed 13mph and 3,800 RPM.
    I was finally able to get rid of the missfire at idle by replacing the whole mag plate. I think my old magplate boss was either too worn, or I had a bad plug wire, despite them testing good. I was running the stock 9×10 prop and I just purchased and tested a new 9×9 prop and didn’t notice any difference.
    The slowness is not due to the boat, I put a 1990 15hp evinrude on the same boat and hit 20mph. The motor will rev all the way to 5,400 RPM or so in neutral. I don’t like reving the motor with no load on it, but I did make a video showing it reving that high.
    The motor appears to be running on the rich side at WOT. I’m running a 40:1 mix. The boat leaves a trail of smoke the entire time it’s running at WOT. I’ve removed the main jet from the carb and it appears to be the stock size and unmolested. I compared it to the jet from my old carb and the diamter matches, but there are two additional holes in the emulsion tube. The holes in the emulsion tube do not play a role at WOT though.
    **Something I noticed today is that the intake manifold stays very cold and sweats. This is with outside temperatures around 90 degrees. The intake is cold to the touch. I know fuel has a cooling effect on the engine and it’s flowing into the engine in a fine mist, but it’s not exactly changing from a liquid to a gas so I’m not sure why it’s cooling the intake so much. I’ve included some photos showing the sweat on the intake. **
    13-14mph is what I’m getting. The max RPM I’ve seen is 4,000 but only for a minute or so max. It stays between 3,700 and 3,800 RPM mostly.

    One thing I forgot to mention. I am getting max timing, and max throttle from the carb. I even disconnected the linkage and operated them independently from each other.

    Avatar
    mikesea7

    Replies: 58
    Topics: 12
    #65813

    Just some thoughts I hope it might help you out. What oil are you using? Sure sounds like it gets tight under load could it be in the tower or prop gears starting to tighten up? Outside high humidity will show up on your intake just you you are showing in the picture.
    Does it use a lot of gasoline? It does not have to use a lot more gas if the mixture is very rich. What color is the smoke coming out of the engine? Black or Blue? You started with good rings and pistons a couple of times now it sure sounds like you have washed the cylinder walls down with excess raw gasoline causing the scuffing the pistons. This is very easy to do and can happen in just a very few minutes of running time. This has happened to me once a long time ago and have seen it since really many times. Many times it came back to a bad carb. By the time the fuel wash carb problem was fixed the engine had highly polished cylinders in the upper ring travel. Cross hatch LOOKS perfect but feeling it ….was a smooth as GLASS. Or If overheating in the combustion space, this will cause the pistons to over expand and the cause of the scuffing and low rpm. Three different power heads? Same tower?
    One more thought is there anyway the port timing could be off?

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65814

    3 different power heads: I never ran the original powerhead on a boat. The ebay powerhead I did run on the boat, it had a bad missfire at idle, but cleared up at nigher RPMs. The piston scoring was done before I got the powerhead. Same for the 3rd powerhead, I inspected it before running it. The pistons were not damaged by me.

    I’m running penzoil TC3 oil at 40:1. The smoke is blue. i’ve never seen anything but blue from a 2 stroke. It does consume a ton of fuel, I think it uses more than it should but I don’t have any experience with these small motors. I’ve never heard of gas washing out rings on a 2 stroke, that’s more of a 4 stroke thing. The port timing can’t be the issue.. these are simple crossflow motors, no has messed with the porting on either of the two powerheads I’ve fun.

    Avatar
    mikesea7

    Replies: 58
    Topics: 12
    #65817

    Miss understood on the power heads sorry.
    These things make us lose hair. How about this it just goes FAT? Cross flow pretty simple on Model 2 strokes I have seen the sleeve be installed backwards and gives you just what you have. But your sleeves are made into the block correct? What was the oil % the engine was built to run on? I think I would try it as nothing could get hurt. One other thing FREE revving will not show up an ignition problem under load. I have been there too.
    I am glad these engine are fun and not brain surgeries.
    All we need is 1. compression, 2. air mixed correctly with a fuel and 3. good spark

    frankr
    frankr
    US Member - 1 Year
    Replies: 3939
    Topics: 43
    #65818

    Armature plate rotating to full advance position?

    Ignorance is simply a lack of education. Ignorance can be cured. There is no cure for Stupid.

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65819

    Mike,
    I forgot to address what you said about the gears. Even though I’m "shooting down" some of your comments and suggestions. That does not mean I do no appreciate them. I need someone else to be thinking of things I haven’t thought of and that’s exactly what you are doing. Back to the gears, I’ve had the gear set out a couple times. Once when I replaced the seals, and again later when I replaced the shift dog. The shaft, gears and bearings all looked good. I was able to turn the driveshaft by hand wiht it in forward or reverse until I installed the impeller, then it was too hard to turn by hand. I believe the factory recommended mixture is 40:1. The older 18hp motors with the clamshell cowls require 25:1 because they run clamshell bearings instead of needle bearings.

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65820
    quote FrankR:

    Armature plate rotating to full advance position?

    Yes it is, going all the way to the stop.

    Avatar
    chris-p
    Canada Member - 1 Year
    Replies: 2444
    Topics: 157
    #65821

    edit

    Avatar
    chris-p
    Canada Member - 1 Year
    Replies: 2444
    Topics: 157
    #65822

    Pull off one plug wire at a time (with insulated pliers of course!) while running. You should hear NOTICABLE RPM drop. If not, you are not running on that cylinder. Sounds like half power to me.

    Avatar
    mikesea7

    Replies: 58
    Topics: 12
    #65823

    Good one Chris

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65824

    Chris I tried that. I can only get to about 7mph on one cylinder.

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65828
    quote MikeSea7:

    Miss understood on the power heads sorry.
    These things make us lose hair. How about this it just goes FAT? Cross flow pretty simple on Model 2 strokes I have seen the sleeve be installed backwards and gives you just what you have. But your sleeves are made into the block correct? What was the oil % the engine was built to run on? I think I would try it as nothing could get hurt. One other thing FREE revving will not show up an ignition problem under load. I have been there too.
    I am glad these engine are fun and not brain surgeries.
    All we need is 1. compression, 2. air mixed correctly with a fuel and 3. good spark

    It’s an iron sleeve in an aluminum block but the last two powerheads ran the same top speed.

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65829

    I found this post. The guy is running 4200 RPM on a 16′ boat. My boat is 14′

    http://forums.iboats.com/forum/engine-r … hp-max-rpm

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65830

    another guy with the same problem as me.

    http://forums.iboats.com/forum/engine-r … g-full-rpm

    Avatar
    stephenspann27

    Replies: 86
    Topics: 2
    #65831

    http://forums.iboats.com/forum/engine-r … at-top-end

    The above link, a guy with the older style carb was getting a max of 13mph until he leaned the high speed mixture.

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