Logo
FULL SITE MENU

115 hp Yamaha fuel mixture adjustment

L

lander12

Contributing Member
Hello to the group. I recently bought a 2000 Yamaha 4 cylinder 2 stroke outboard 115 hp model C115TLRY using 50:1 premix into twin carbs for my 18 foot Sunbird cuddy. I used premium fuel with no ethanol and semi-synthetic 2 stroke oil. Today I took it onto the water for it's first cruise. All went very well for the 20 minute cruise at various speeds but heading back to the dock for loading, I noticed that it seemed smoky (even while warm) and at least 1 spark plug was occasionally mis-firing. It seemed to use quite a lot of fuel. When I got home, I pulled all 4 spark plugs and all of them seemed wet. The plugs were NGK BR8HS-10 and specs call for B8HS-10. Is it possible that the carbs are running too rich and the mixture screws need to be adjusted? Are the different spark plugs an issue? My experience with smaller 2 stroke outboards is that they are smoky on startup but become less so when warm.

Any thoughts/previous experience/ advice appreciated. Thanks in advance.
 
Last edited:
For some reason those carb'd 115's seem to be much thirstier than you would expect. I have come across this numerous times and no one I know of has ever got one to run as economically as they would like. Nice solid engine, but thirsty.
 
OK Chris. I hope to get through this year's boating season without cleaning the carbs since we're getting near the end anyway. I will switch to Yamalube and Yamaha Ring Free in the fuel. Many thanks for the reply.
 
I won't be running the outboard full bore; today I cruised comfortably around 20 mph at 3000 RPM. I'll clean the carbs the first chance I get. Hopefully all this will allow me to max out the fuel economy. I'll have to live with what it turns out to be.
 
The fuel issue with these outboards is probably a thread of it's own and may very well be addressed elsewhere, but are there obvious things that can be done to improve fuel economy? On the exploded diagram of the carb, the main jet is a replaceable item. Is there a smaller diameter main jet available from Yamaha? To me, the smokiness and wet spark plugs is a clear indication that the motor is drowning in fuel. A link to a fix for this issue (if it exists) or any thoughts would be greatly appreciated.
 
I never recommend changing jet sizes ever! End of story! If you lean out a cylinder it will kill the powerhead. Yeah you might save a few bucks. then you get to spend a couple thousand bucks to have your powerhead rebuilt! It is like using cheap oil; It is just a bad plan. Lander, buy a can of powertune from your dealer. take out the bleed screws (out of carbs) and spray the powertune in. This might band-aid the issue, but it might cause a clog. Again if it is running rich i might be okay with that and leave well enough alone. You can also give it the old touch test to find out. lightly touch the outside of the head (near the spark plugs) Is one cylinder hotter than the others?
 
Back
Top