15hp 2 stroke Yamaha tiller

Joined
Mar 25, 2010
Messages
2
I am new here and would like to say hello. I am working on a gheenoe/yamaha 15hp 2 stroke tiller makeover and yesterday I ran into a little road bump.

Ill ask my question first and then tell you all a "funny" story that happened to me yesterday.
Upon taking my new 04 yamaha 15hp 2 stroke out for the first time, I ran into a funny sound. It seems to only make the noise while doing anything above idle (not while idling) and anything under 3/4 wot and above. It doesn't seem to do it once the motor hits a certain speed which is pretty fast but managable. The sound isn't really loud but you can hear it. Its like ......dunk...........dunk.dunk..........................dunk.................dunk...........dunk...dunk....... You can see the motor twitch just a hair when it makes the sound? ANY ideas? Could this be normal?

I also noticed idle and a little above seems to vibrate pretty good but it may be normal?? New to yamaha. Any help would be greatly appreciated.

Funny story:
Im only telling this story to save someone else from making the same mistake. We are all very fragile and a wrong move can be deadly. I've had a 6hp merc on the gheenoe for a while and it pushed along great with one person. Yesterday I overhauled the transom and took step by step pics. I was hoping to post them to a few sites to give some guys an idea on how to use starboard as a transom and how not to be afraid to rip that old rotten wood out. Upon completion I threw my recently acquired yamaha 15hp on and ran down to the local creek for a quick trial :eek::eek::eek::eek::eek:

I decided to try to make a small video while hoping up on plane and entering the fourth dimension, bad idea. First off, holding the camera took a hand of the boat. Second, I had only a couple runs experience with the new motor. Anyway, I was hauling arse and as soon as I came off plane I got the wobbles. My foot slipped, tiller went completely sideways, so did boat, camera went overboard with all the pics, I **** my pants, boat almost slammed into the shore..... Very scary! It taught me a very strong lesson. Don't take these machines lightly, they are not toys, they can kill you. I will say that I think most other boats would have flipped. I dont know how the gheenoe didn't flip, but it didn't!?! WOW!!!! Almost died!

Please let me know if you can help with the motor issue.

Thanks
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,195
Re: 15hp 2 stroke Yamaha tiller

sounds like a lean sneeze. you may need to pull and clean the carb.
It never hurts to make sure the pistons are not eaten because of lean running cylinders.
If you do not know the maintenance history of a motor then change water pump and thermostat, check or replace the fuel pump, and check the compression. At least then you know what you started out with.
 
Joined
Mar 25, 2010
Messages
2
Re: 15hp 2 stroke Yamaha tiller

Is there any "easy" way to tell if the pistons are eaten? Motor seems to have plenty of power. Would there be signs on the plugs? Plugs look like milk chocolate. Guy told me the water pump was changed about a year ago. Not sure about fuel pump. I'll try to find out.
Thanks
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,195
Re: 15hp 2 stroke Yamaha tiller

You can check compression. But what I meant was do not keep running it if it has a problem with running lean. clean the carbs.
 
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