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  • Monte NZ

    International Member - 2 Years
    Replies: 304
    Topics: 89
    #229964

    Hi All.
    I am trying to help my elderly neighbour fix his 2015 2hp Yamaha which just will not idle!
    I realise that the motor is very modern compared to what out members generally work on, but I was hoping that someone may have had experience with these motors and may be able to
    offer some advice.

    The motor starts and runs well at high speed and interim speeds, but dies out when you try to throttle down to idle.
    We have lost count of the number of times we have taken the carburetor apart and cleaned all the components with compressed air etc…….the float level is fixed and can’t be adjusted.

    The motor is in very tidy condition. The carb is very simple design, with the only adjustment being a screw that controls the rise and fall of the piston holding the needle ………this is to obtain idle speed.

    The position of the needle in the piston inside the piston is correct………can be adjusted by a cer clip.
    It’s worth mentioning too that the carb design is very similar to those used on the British Seagull motors;.

    The O ring is in the correct position……..this acts as a seal where the carb is mounted on the intake manifold.

    The reed valve has been taken out and checked and appears ok

    Compression is very good at 100lbs with plenty of bounce when flicking the flywheel over.

    The ignition system is a sealed unit without points and delivers a very healthy blue spark.

    The fuel tank and lines have been completely flushed.

    I have looked at You Tube of these motors running which shows them idling beautifully.

    Many thanks in advance for any help.

    Monte NZ


    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #229966

    tried pumping the bulb while poorly idling ?? if better = bad fuel pump, sucking air somewhere instead of fuel check fittings gaskets needle packings etc….

    lift the gas tank above the engine before reducing speed to idle = if better = fuel issue see above 🙂

    Joining AOMCI has priviledges 🙂


    mas

    US Member - 2 Years
    Replies: 192
    Topics: 43
    #229968

    …also, make sure the backside butterfly valve (throttle plate) is completely closed at idle. I had a new 4hp Yamaha that had similar symptoms and finally found the throttle plate was cracked slightly opened.

    Mas


    cajuncook1


    Replies: 842
    Topics: 72
    #230013

    I don’t know the model number of the motor, but it looks like Yamaha made a 2.5hp motor in 2015. I was reading in the owners manual about internal fuel filters. If the the fuel filter has some debris in it, it could affect fuel delivery. At higher speeds it may not be noticed but at lower speeds/idle fuel delivery maybe impaired. Sorry, I do not have experience with the Year, Make and Hp of the motor.

    It just seems like the issue is fuel delivery.

    Here is a link to what I believe is a owners manual for your neighbor’s motor. Page 83 reviewed filters and maintenance.

    https://outboards.yamaha-owners-manuals.com/om/LIT-18626-10-21.pdf

    Cheers,

    Cajun

    BB72180F-1F98-4CA9-963F-7C49D66D38F4


    fleetwin

    US Member - 2 Years
    Replies: 4737
    Topics: 46
    #230016

    Not familiar with this engine, so can’t help much with specifics….The carburetor might look simple, but I am assuming this is a 4 stroke engine… When was the last time the engine idled correctly for the owner? Did it sit after that with gas still in the carb? Was the carb dirty/fouled fuel when you pulled it apart the first time? Are you sure it isn’t losing spark at low speeds? You might want to put one of those inline neon spark testers between the plug and the coil wire and monitor it while trying to make the engine idle. All that being said, did you try a new spark plug?


    DAN UMBARGER

    US Member - 2 Years
    Replies: 207
    Topics: 28
    #230023

    I was also going to say a new plug first then make sure the carb IS clean. Sounds to me like the low speed system is still plugged. The 4 stroke motors have VERY small jets and not sure about the 2 hp’s but all the Japanese motors use pilot jets and almost all the 4 stroke carbs I rebuild have the pilot jets plugged up. They need to be soaked and blown out. I use OMC engine tuner to soak all my 2 & 4 stroke carbs then spray with carb cleaner and blow out with air.


    rudderless


    Replies: 159
    Topics: 5
    #230040

    I bought new a 2006 f2.5..in 2006. Used it every day, 7 days a week from april1 to nov 15….until I wore it out in 2014. So I am a bit confused by the reed valve and slide valve carb referral. Sliders usually have a fixed low jet with adjustable air screw. Butterfly usually have a low adjustment for fuel. The butterfly carb on mine had a fixed low jet with air screw.

    As soon as I started mine I knew I had to find the plug that hides the low air adjustment as it barely would idle. Also the high jet was too small for proper operation. Remember they are jetted to pass emissions…not for optimum operation.

    I found the plug that hides the low adjustment air screw. Drilled a small hole through the plug..carefully so as not to drill into the adjustment screw. 1/2 turn clockwise to cut some air with an eye glass screwdriver made it a whole nother motor.

    …and yes that low jet is very small and is probably plugged as mine would be plugged about every other year upon spring startup even though I ran it dry in November. Ya need to pass something through the jet to confirm its open.

    The end for my f2.5 came in 2014 as it started to blow oil out of the crankcase from blowby…even though I changed the oil constantly with premium oil.

    All this assuming your 2015 is like my 2006. Looks like it is…

    So in closing find the low speed air screw plug…mod it so ya can adjust it properly….remove the low jet, clean the jet and make sure its open…don’t guess.


    Monte NZ

    International Member - 2 Years
    Replies: 304
    Topics: 89
    #230044

    Thanks crosbyman, mas, Cajun, fleetwin, Dan Umbarger and rudderless for your replies……..much appreciated.
    Reading your replies I can see unfortunately that I slipped up badly in not explaining that the motor is a 2 stroke Yamaha and not a 4 stroke,
    so please accept my apologies for this oversight.

    I can see now that I should have put the model number ……..would have made things a lot clearer and saved you time and trouble. Again my apologies!
    Here in NZ we have lots of small 2 strokes and in fact you can still buy new small 2hp 2 stroke Yamaha outboards as well as other brands.
    How much longer for, remains to be seen. I think Tohatsu is the major manufacturer for Mercury etc these days.

    The motor model number is 2CMH.

    I would like to add that the fuel tank and line has been thoroughly flushed out and as I mentioned previously, every component of the carb has been taken apart and cleaned and then blown through with my compressor.

    We feel that it be a fuel problem because of the way the motor just peters out when you get to the idle position..
    We have also tried another (new) sparkplug……..no improvement.

    Any other ideas will be much appreciated.

    Thanks very much once again.

    Monte NZ

    The carb doesn’t have any butterflies in it’s construction, only the cylindrical piston carrying an adjustable brass needle.


    billw

    US Member - 2 Years
    Replies: 2071
    Topics: 66
    #230045

    I know the type motor you mean. A couple of ideas:

    Let the motor just sit there, not running and see if fuel eventually drips from the carb, meaning that the float valve might leak a bit.

    Run the motor, let it idle and die on it’s own and look at the plug, to see if it seems more wet or dry.

    Make sure the idle exhaust relief holes are nice and clear.

    Make doubly sure that the carb is pushed fully onto it’s mounting flange, tight against the o-ring, before the pinch clamp is tightened.

    Do you have a manual for it? I think I have one for an identical Mariner unit, someplace. I will check; but if I recall, they are not even supposed to idle below like, 900 RPM or something. Also, are you sure the e-ring on the throttle plunger needle is in the right spot, per a manual?

    Beyond that, I am starting to worry about the lower crank seal….

    Long live American manufacturing!

    • This reply was modified 3 years, 1 month ago by billw.
    • This reply was modified 3 years, 1 month ago by billw.

    crosbyman

    Canada Member - 2 Years
    Replies: 3588
    Topics: 326
    #230049

    ok it may be simple….like my snowblower problem…. run a decarb/tuner product like MercPower Tune or a half or full can of Seafoam costs a few $$$ may solve the issue.

    have you tried pumping the bulb while it dies ?? yes no ?

    it is starving either it is not sucking fuel (bad crankcase seals has suggested by billw causing a vacum loss needed to suck the fuel out of the carb jet) or fuel flow is restricted….help it (tried lifting the tank above the motor while it dies yes-no ?

    Joining AOMCI has priviledges 🙂

    • This reply was modified 3 years, 1 month ago by crosbyman.
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