I went out this morning and boat running like a top. After running about half the day ,I was on a run back up the river when my rpm, fell off to around 4500 . I stopped and restarted boat hopped right up on plane and came to full rpm's on pad and then thirty seconds after it fell back to 4500 r.p.m.'s . I then began to worry and shut down engine and pulled cowling to check for any visual problems and found none. motor would then not restart. After trying to start for some time i finnally gave up and trimmed motor up and was going to use trolling motor to come in. but with motor trimmed up engine fired right up. dropped it back down and headed for the ramp, motor still dropping r.p.m's to about 4500. even though it is a 2006 it only has 76 hours on it and I run ring free and stabil on every tank as recommended. I am a heavy equipment technician and know my way around a multimeter and wrenches. just wanted some help from you guys that seem to know these engines so well. any pointers on where I should start. motor still has factory warranty but I am afraid to take it in because of some post I read saying yamaha would not cover fuel related problems. water seperator changed in last 5 hours. Any help would be much apperciated.
Had similar problem. Try changing fuel filters. Should have three (3). One external water seperato/filter and two (2) on engine itself. We found out about the third one the hard way! It's in the high pressure system.
monitor the fuel pressures to see if they are dropping( VST & rail), that should give you an idea of where the restriction is. high pressure pump screen or the pre filter would be my guess at this point