15hp 2 stroke yamaha outboard

[pritch]

On a 15hp 2 stroke Yamaha outboard what are the 2 small rubber pipes for, that are attached to the cylinders. One goes to the reed valve block, and the other ???????

[robert graham]

Without a photo, my first guess would be those small black rubber oil circulation lines that move oil from various areas to others improving lubrication....

[pritch]

thank you Robert

[pritch]

Hello Robert, may be you can offer some advice to me about my 15hp 2 stroke Yamaha outboard. My problem is that when I start the outboard it will idle OK, but when I advance the throttle the engine will run rough and cut out. I have replaced the Carburettor, CDI unit, high tension coils and leads ( all off another motor that is functioning quite well) and the same problem occurs. I would appreciate any advice on how to eliminate the problem. It becoming quite frustrating. I would appreciate any help that you can offer.

[racerone]

First thing is a compression test.

[pritch]

compression all OK

[pritch]

any further suggestions anyone?

[QBhoy]

Almost certainly a carb related issue. Give her a clean out. Jets too.

[Mohawkmtrs]

Regarding the rubber "pipes" (hoses) you spoke of in Post #1, I believe you attached the top hose correctly if, when installed, the hose should be practically level (horizontal).

The lower hose fits onto a nipple located at the very bottom of the crankcase assembly (below the reed block) and behind the shift arm shaft.

Connecting this hose may eliminate your running rough above idle issue.

[QBhoy]

Not sure this engine has oil lines.

[racerone]

QBhoy-----Are you not aware that most 2 strokes have an oil recirculation system ?------Some motors use wee hoses and some use internal passageways !!

[QBhoy]

QBhoy-----Are you not aware that most 2 strokes have an oil recirculation system ?------Some motors use wee hoses and some use internal passageways !!

I’m aware that oil injection models do. Maybe wrong but I’ve never seen a 15hp oil injection on a Yamaha ??

[QBhoy]

Please tell me if I’m wrong.
All the best.

[racerone]

Sorry you are wrong..----Time for you to look this up.-----The regular premix models have hoses to RECIRCULATE oil.-----Many 2 stroke motors also have internal passages to do the same thing !!

[QBhoy]

Apologies but how would it separate the oil from the fuel to circulate ? Or do you mean it recirculates the fuel ?
I’m confused. I’ll look it up. All the best.