Yamaha 115 2 S problem

[davej]

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.

It’s fine below 2k but it wants to shake its to bits above that, now what’s wrong with it? It ticks over fine, my thinking is it’s 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

[John hulme]

Originally Posted by davej

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.



It’s fine below 2k but it wants to shake its to bits above that, now what’s wrong with it? It ticks over fine, my thinking is it’s 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

[matata]

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

[davej]

Thank you for the input, no it doesn’t 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. It’s 27 yrs old and they are original so need doing whatever. We did the switch box 4 yrs ago, so hopefully it’s 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 wasn’t working inside the packs. Well thats my theory, at least at the weekend we will know for sure!

Thanks

Dave

[matata]

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

[Davie]

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.

[A1an]

Originally Posted by davej

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 it’s 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

[neil.mccrirrick]

Get one of these to see if your coil or plug is breaking down

https://www.ebay.co.uk/itm/111987068352

[davej]

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 haven’t 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.

It’s 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

[davej]

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 it’s 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 didn’t get round to it, it’s 27 yrs old so it’s time it was done and had transformed the engine.