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  1. #1

    Default Evinrude won't idle at shifting RPM

    I just purchased a 1980 Evinrude 25 HP with tiller steering and throttle. After lubing the cylinders and cleaning the carb the motor started effortlessly. There are a few minor issues to deal with, the first of which is the fact that the motor dies when I idle down to the shift RPM level. I have no idea how long the unit sat before I bought it. The motor sounds so strong with the throttle open, or even just a little bit open, but I obviously can't even test the gear box when I can't shift it. There is a strong stream of water being expelled by the impeller, and it was really smokey at first until the extra lube oil burned off. We've tried adjusting the lean/rich screw all through its travel, but with only minor difference. Is there any other way to adjust a 2 stroke carb? I had to jury rig the fuel supply by hooking directly into the fuel pump(I don't have a fitting). Could this be a part of the problem? What else could I check? Sorry to ask so many questions, but this is only my second outboard motor and my first 2 stroke. Thanks for your help!!

  2. #2
    Join Date
    Oct 2011
    Location
    maplevalley WA
    Posts
    7,602

    Default Re: Evinrude won't idle at shifting RPM

    Check it has good compression and the spark jumps a gap of 1/2 inch minimum. You can make a spark gap tester or get one at the part store. Turn the slow speed needle in to lightly seated and count the turns out 1 1/2 turns, make sure it is in neutral and give it throttle to the high idle stop. start it and let it fully warm up and make sure the choke is all the way open then slowly drop the engine speed to around 700 rpm if you can and then put it in gear in the water slowly adjust the slow adjustment on the carb out until the engine loads up the turn it in until it starts to cut out then back out for a smooth idle. Wait about 10-15 seconds between adjustments for the crankcase to stabilize one you find a nice idl add 1/4 turn rich to protect the engine from a lean condition. Give us the compression numbers and spark gap and we will go from there.

  3. #3
    Join Date
    Oct 2011
    Location
    maplevalley WA
    Posts
    7,602

    Default Re: Evinrude won't idle at shifting RPM

    The quick disconnects for the fuel line is nice for filling the tank but not necessary as long as it aint sucking water or air, is the tank clean. Did you change the spark plugs and you can check if it shifts without the engine running just spin the prop while shifting, drain the gearbox and look for water or metal shavings. If the oil looks good fill it from the bottom until oil comes out the vent hole on top put the top plug in and then the bottom plug. Then pull the top plug and top it offf.

  4. #4
    Join Date
    Oct 2011
    Location
    maplevalley WA
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    7,602

    Default Re: Evinrude won't idle at shifting RPM

    The knob on the slow adjust just pull off so you can turn it clockwise to the lightly seated position and the turn it out to 1 1/2 turns and adjust from there.

  5. #5

    Default Re: Evinrude won't idle at shifting RPM

    First of all sir, thank you for your help. I have recorded compression 110psi on both cylinders and the pressure held for quite some time before being released. Some of the Youtube videos on this subject present a wide range of readings as being "good" compression. What is good for my motor? The other thing you said I should test was the spark, and it jumped half an inch easy. What is the actaul plug gap for this motor? Would new plugs be a good call? When you talk about the "slow adjust" you mean the rich/lean screw right? There are no other adjustment points on this carb, are there, without doing something internal? How about a carb rebuild? Please remember that the motor started very easily. Anyway, thanks again, and I look forward to hearing your response and following your advice.

  6. #6
    Join Date
    Oct 2011
    Location
    maplevalley WA
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    7,602

    Default Re: Evinrude won't idle at shifting RPM

    If your numbers are within 10% and above 90 compression is just fine and plug gap is .040. Yes the hi-low knob is the idle air mix I allways just pop it off with a screwdriver and turn it all the way clockwise until it lightly stops and count the turns ccw 1 1/2 turns and adjust from there once you dial it in center the knob between stops and snap it back on. Dont forget to add a 1/4 turn ccw (rich) before you center the knob.

  7. #7

    Default Re: Evinrude won't idle at shifting RPM

    Wow, I am pretty confused by this, guys. I've tried adjusting everything, but my son noticed that the rubber retainer on on the air idle screw has the square tab broken off. The broken off tab is still in its slot, but could this be a way that it is sucking air? The retainer is available, but should I get a whole rebuild kit? Would there be any value in a fuel pump rebuild? Thanks again!

  8. #8
    Join Date
    Oct 2011
    Location
    maplevalley WA
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    7,602

    Default Re: Evinrude won't idle at shifting RPM

    It never hurts to go through the fuel system complete, replace all the fuel lines rebuild the carb and fuel pump. I suppose it could be sucking air there but not much it is still a good idea to replace anything out of order. You can allways try the seafoam trick, run the engine out of fuel and pump the carb full of seafoam and let sit overnight. The next day running in water hook the fuel line up to the tank and start the engine and run at around 2000 rpm until the smoke stops and then try and adjust the low speed knob. Be sure and preset the knob at 1 1/2 turns out from lightly seated and wait 15 seconds between adjustments. SAlowly turn it out until the engine loads up (coughs) and slowly turn it in until it starts to cut out then back out for a smooth idle and then add 1/4 turn rich CCW and center the knob stop to stop. You want to adjust the idle speed to 700 rpm or a nice slow idle in gear in the water.

  9. #9
    Join Date
    Oct 2011
    Location
    maplevalley WA
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    Default Re: Evinrude won't idle at shifting RPM

    Have you messed with the idle stop screw it is item # 85 it keeps the advance from going too low that could be part of your problem turn it in so the motor runs about 800 rpm adjust the low spped idle and the back off on the rpm and adjust the low speed screw again.

    http://www.marineengine.com/parts/jo...t+Housing+-+25

  10. #10
    Join Date
    Oct 2011
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    maplevalley WA
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    Default Re: Evinrude won't idle at shifting RPM

    Sorry item #84

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