Re: Yamaha F115 inconsistent rpms over 3000 rpm
I had a similar problem with my 2006 F90. In my case it turned out to be partial clogging of the in-line fuel filter between the low pressure fuel pump and the VST. (The root cause was gunk in the fuel caused by the presence of water.) Some fuel was flowing, but not enough. The fuel line arrangement on the F115 is probably a little bit different, but the principle is the same - put a little restriction ANYWHERE in the line and you can get some - but not enough - fuel flow.
With the engine off, you can disconnect the low pressure line where it enters into the VST and pump the primer bulb to see how much flow you have. On my engine, it was difficult to squeeze the primer bulb and the fuel flow was minimal. Restrictions can occur anywhere in the line from the anti-siphon valve on the tank through the fuel filter(s) and pump(s).
I would assume a fuel pump could also cause this problem. I don't know, however, if a faulty fuel pressure regulator would cause these symptoms or not. You might also check all fuel line connections from the tank to the fuel pump to make sure none are sucking in air. Hope this helps - Woodnaut.
