Yamaha F75D engine sputtering - FUEL?

[Panama Ron]

I have a 2005 Yamaha F75D fuel injected outboard. Recdently had a problem of cutting out and sputtering at higher RPM's which I believed was a fuel problem. When I backed off to about 2000 RPM it settled down for a while then quit. The engine would always start right back up afterwards. Thought is was water in the fuel. Did not have a fuel seperator so ordered one. Then disconnected the built-in tank and installed a portable 6 gal tank to eliminate that possibility of water in the fuel tank. Ran OK for 1 week then same problem. Checked the fuel filter after it shut down, still had full fuel and no water in the bowl. Replaced the squeeze bulb and fuel line after a small leak found. No change. Checked all wiring and sensors, no problem found. Changed oil and filter thinking something was clogged causing the engine to shut down.

Only thing I can think of is the fuel pump, but I really know very little. Any of you "smarter than me and way more experienced" guys have any other ideas? I am stranded on an island in Panama!!!!

 

[Woodnaut]

Re: Yamaha F75D engine sputtering - FUEL?

Pananma, I have a 2006 F90 which I think is a similar engine in many aspects. Last year I had a problem that was similar - The engine was running fine at the dock and underway at lower RPMs. At higher speeds, however, it would dog out, sputter, and act like it was going to die. The original cause of all of my problems was water in the gas which caused all sorts of problems throughout the entire fuel system. I disassembled the entire system and thought I had cleaned everything out really well, but the problem soon surfaced again. It turned out that there is a small in-line fuel filter between the low-pressure fuel pump (on the back of the engine) and the VST on the side of the engine. This filter was not properly cleaned (or replaced). This filter was partially - but not completely - plugged. It was only letting a very small amount of fuel trickle through. It was enough to fill up the VST at idle and low speeds. Once I throttled up, however, the fuel supply rate was just to low to keep things going and the engine would start cutting out. If I went back to a lower throttle setting, the engine came back to life.

The fix was very simple. Since I didn't have a replacement, I pulled out the small in-line filter and flowed backwards through it with some gasoline. A bunch of crud immediately came out of it. I reinstalled it and it was like I had my new engine back. Again, this filter is located in the line from the low pressure fuel pump (in the back) to the VST on the side. It is cylindrical and is mounted in a black plastic sheath.

The bottom line on this was a restriction in the fuel line. I would imagine a restriction anywhere, or an improperly functioning fuel pump might produce similar results. Hope this helps.