F115 Throttle Problem

[Skiff Skipper]

Hello All,

I am new to this forum so if this problem has been addressed, please let me know. I have a 2010 Carolina Skiff with a Yamaha F115 4 stroke motor. It has been in the shop 4 times in the past 2 weeks for a power issue. When I attempt to go full throttle, I bury the stick and I only get 3800 RPM @ 10MPH max. The filters and separator has been changed 3 times, the plugs twice and the injectors have been cleaned. When I get it back from the shop, each time it runs great for a day and then if I put fresh gas in the tank, it bogs down again. It has a Yamaha water separator on it and all OEM parts. The motor has about 20 hrs on it total. When I check the water separator, I found small white milky bubbles in the fuel, but no water at the bottom of the jar. Any Help would be greatly appreciated because the guys at the marina are baffled too.

Thanks

[ausnoelm]

I guess the easiest test is to run from a remote tank with fresh known good fuel to isolate your tank in the boat, makes no difference how many times you clean the fuel system, if you have crap fuel in your tank, you will need to clean it all again if you use the same fuel and tank.

[Skiff Skipper]

F115 Throttle Problem

The funny thing is, that was done and the motor ran great. They then put 20 gallons of fresh fuel in my tank and ran the boat for 3 hours under load and the boat ran great. I water tested the boat myself for an hour with their gas and the boat ran great. I then took the boat out of the water and trailered it 20 miles, and put 17 gallons of 93 octane fuel in the tank and trailered it to the launch. As soon as it hit the water, the problem was back.

[rodbolt17]

quit with the 93 octane, waste of money,
do carefully inspect the tank.
we are and have found the translucent skiff tanks IF exposed to sunlight and E fuels. the tank,fuel sender float AND draw tube disentergrate.

[Skiff Skipper]

Hey Rodbolt,

Thank you, I appreciate the advice and I will stop fueling with 93, but the tank is aluminum and it is below the deck with a secured hatch plate over it so it is not exposed to sunlight at all. Waiting to see what the Yamaha Rep. has to say about it. I will post the results as soon as I get them.

[rodbolt17]

If you actually talk to a Yamaha rep, they are going to tell you to fix the hull fuel issue.
them small milky bubbles are the result of phase separation and most likely the entire fuel system is contaminated again and will require recleanng.

until you get whatever is drifting about in the bottom of the tank and on the fuel line walls ths issue will reoccur.

that's the beauty of our marine technician stimulous fuel program.

E fuels,once they absorb water, cannot be filtered with conventional water seperators.

however once under the hood engine heat causes the two to separate faster, that's when the bad ju ju really starts.

gotta love our govt.

[kyleroberts1943@yahoo.com]

I have had the same problems with my 115 four stroke. I removed my built in tank and replaced the fuel feed lines. Flushed my vapor separator. Little bleed line on the bottom to drain trash and water. The final thing that fixed my problem was dirty fuel injector filters. Found a place in Long Island New York that will rebuild your injectors or sell rebuilt ones for 39 dollars a piece.Now my motor runs full speed. For some reason I have not seen dirty fuel injector filters mentioned by any Yamaha people.

[rodbolt17]

I have mentioned them till I am blue in the face.
ALL Yamaha injectors had a screen when they left the factory.
some repair shops remove them.