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Old 21 June 2021, 13:43   #1
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Yamaha 115 2 S problem

Hello All,

My 115 2S Yamaha C 1994 had just developed a problem, after its mega day out last week circumnavigating Mull, the following day after a short run to a dive site ok, it developed rough running and vibration about 2000 rpm.

Itís fine below 2k but it wants to shake its to bits above that, now whatís wrong with it? It ticks over fine, my thinking is itís a coil, any idea how to test them or should I just buy four new ones and install them?

The fuel pump was replaced last year and I have changed all the fuel filters when we serviced it before this seasons use.

Thank you for any help you can give.

Dave
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Old 21 June 2021, 15:15   #2
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Originally Posted by davej View Post
Hello All,



My 115 2S Yamaha C 1994 had just developed a problem, after its mega day out last week circumnavigating Mull, the following day after a short run to a dive site ok, it developed rough running and vibration about 2000 rpm.



Itís fine below 2k but it wants to shake its to bits above that, now whatís wrong with it? It ticks over fine, my thinking is itís a coil, any idea how to test them or should I just buy four new ones and install them?



The fuel pump was replaced last year and I have changed all the fuel filters when we serviced it before this seasons use.



Thank you for any help you can give.



Dave


Have you checked the prop ? It could be damaged or loose
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Old 21 June 2021, 15:47   #3
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Does it do it on the land on the muffs with no load? I would have thought with modern clamp meters it would be able to diagnosed a missing cylinder no probs. Do any of the plugs look different.? Sounds very electrical..Nik
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Old 22 June 2021, 05:59   #4
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Thank you for the input, no it doesnít do it on land on the muffs and seems to run normally up to 2 k and I agree it sounds electrical and as we have been discussing replacing the coils for some time have decided to do that. Itís 27 yrs old and they are original so need doing whatever. We did the switch box 4 yrs ago, so hopefully itís not that again.

The prop is fine.

My logic is that after our mega trip around mull when the engine ran for a good 5 / 6 hours and clearly got hot, that was the last straw for a coil and the next day out it ran ok a short distance but on the way home it again had got hot and the insulation just wasnít working inside the packs. Well thats my theory, at least at the weekend we will know for sure!

Thanks

Dave
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Old 22 June 2021, 13:27   #5
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Just before you part with your £ do a quick compression check..If all ok and you cherish the engine ( nice engine by the way) Id treat it to all new coils....Theyre prob breaking down under load...Keep me posted..Nik
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Old 22 June 2021, 14:18   #6
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Is there plenty 2 stroke oil in the header tank? Sounds like either the low oil sensor or either of the overheat sensors. Disconnect the pink wire out the cdi unit and see what happens.
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Old 22 June 2021, 14:45   #7
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Quote:
Originally Posted by davej View Post
Hello All,

My 115 2S Yamaha C 1994 had just developed a problem, after its mega day out last week circumnavigating Mull, the following day after a short run to a dive site ok, it developed rough running and vibration about 2000 rpm.

my thinking is itís a coil, any idea how to test them or should I just buy four new ones and install them?


Dave
If you are handy with a ohmmeter you can test the resistance on the primary and secondary sides of the coil. I wouldnt just fire parts at it
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Old 22 June 2021, 14:50   #8
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Get one of these to see if your coil or plug is breaking down

https://www.ebay.co.uk/itm/111987068352
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Old 22 June 2021, 17:21   #9
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Thank you again for the input, the oil is fine and both the engine header tank is full and the main tank is going down. I havenít done a compression check yet but will, hopefully they are all ok.

I will also check the coils with a multi meter and she what the reading is, however, I think they are breaking down under load when it gets hot.

Itís a lovely engine, smooth and with loads of torque, certainly has a drink problem but is an old smoker!

Will keep you posted.

Thanks Dave
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Old 17 July 2021, 05:05   #10
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Just to let everybody know that one of the coils had failed, we took them all off and a primary winding had failed on one of the coils. We have now replaced them all, pretty promptly thanks to Andy at bhg marine and itís like a new engine, smooth to accelerate, idles nicely and potters along as it should. Just ready for its next adventure. Thanks for the advice everyone. It clearly needed doing and we were minded to do but what with lockdowns etc just didnít get round to it, itís 27 yrs old so itís time it was done and had transformed the engine.
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