Yamaha 115 missfire?

[LewisB]

Hi Guys,

This is the first time i've posted, but i've been lurking for a while picking up some great tips.

I'm going to have to pick some brains if you've got the time.....I've got a 1986 yamaha 115 engine on a 5.5m RIB. I can be running along at full throttle, on the plane and then i seem to lose a cylinder, it still stays on the plane but there is definate power loss, it will then suddenly power up again, sometimes in a few seconds, other times a couple of minutes later.

What is your gut feeling for this - is it a blockage in one of the carbs or an intermitant HT lead problem. If it is a carb problem, will an additive cure it?

Thanks in advance for any help you can give me

Lewis

 

[rodbolt]

Re: Yamaha 115 missfire?

cleaning the carbs is quick and easy, replacing the fuel pump periodically is good insurance.
a dvm with a dva adapter can quickly find any ign misfires.

 

[LewisB]

Re: Yamaha 115 missfire?

Thanks for the reply, I'll clean the carb and hope that sorts it out.

Do you think it is more likely the carb then electrical? I feel that if it was electrical it would happen every time the boat goes out - it is happening often but not every time i take her out - frustrating! Am I thinking along the right lines here?

Lewis

 

[drewmitch44]

Re: Yamaha 115 missfire?

i got a 86 yamaha 115. 115ELTJ. Im interested as to how this turns out. I bought mine used and its clean. Ive used it this whole season without problem. Gl Man sounds like its one of those hard to diagnose problems if it only happens periodically. I hate that you think you got it fixed then 2 outings later it happens.

 

[drewmitch44]

Re: Yamaha 115 missfire?

Lewisb do you run straight gas and use your oil injection? or do you premix? You should have that precision blend motor.

 

[LewisB]

Re: Yamaha 115 missfire?

Hi Drew,

I just fill up with petrol (Gas on your side of the pond!) and let the engine do the mixing.

Its a frustraiting problem, but luckily not one that is keeping me off the water. I'll start on cleaning the carb, check the plugs and then move to the HT leads.

Do you know if the HT leads split up so I can buy one and check each cylinder or does the whole lot need to be changed in one go.

And yes, I'm waiting for a service manual turn up!!

Lewis

 

[outdrsmn82]

Re: Yamaha 115 missfire?

how can you sort out ignition problems from spark plugs or fuel issues? is it just a trial and error thing?

 

[rodbolt]

Re: Yamaha 115 missfire?

way old thread.
if your having issues start a new thread.
no its not poke-N-hope its very simple and quick but it does require an investment in manuals,test harness's and meters.
takes 30 min or less to lock it down to fuel or ign.

 

[LewisB]

Re: Yamaha 115 missfire?

Yep, I got this sorted out.

Also its a 1996 engine, not 1986 as I originally mis-typed!

I took the great advice from Rodbolt and many other members of the forums, worked through the service manual looking at fuel/carbs and then invested in a DVM and DVA adapter and did the electrics.

I learnt a hell of a lot and it turned out to be the CDI, haven't had a problem since replacing it.

Hope you've got better boating weather than we have - had force 8 to force 9 for pretty much the last 2 weeks. Crap!

Lew