I'd be really interested and eternally grateful if someone on this forum can get to the bottom of a mechanical issue with the above motor - which 3 different certified mechanics and and a service ticket with Yamaha themselves cannot figure out. <br>I am the second owner of a f75 4 stroke tiller, 2010 motor. I have it inspected and test ran 2 times before buying the rig from an individual who bought this rig new and took really great care of it - or so it seemed. The motor is on an Alumacraft Navigator 175 powermatched rig. It has on the original prop and it is in great condition.<br>When I first bought it, the boat ran at 5500 rpm and about 31-32.5 mph trimmed up (depending on weight in boat at full throttle.) It did so for the first 2.5 years I owned the boat. Then last fall, it stated to run slightly slower and less rpm - like 5300 one day, then the next it was 5500. This really never fluctuated during the same outing and never ran poor overall. I changed plugs my last time out last fall and it ran at 5500. That may have been coincidence, however.<br>This spring it did the same from oner outing to the next and actually stared to drop rpm more more frequently - until a trip in early June this year it just maxed out at 5000 rpm and 27 mph at full throttle and never went back to "normal." In the process of trying to figure it out on my own, I noticed that I could actually get the rpms up to 52-5300 if I backed off the throttle in very small increments and found a "sweet spot" (an estimated 85-90% throttle).<br>I always had the certified shop winterized the rig and always have used stabilizer and Yamalube Ringfree as recommended. So, I called my usual mechanic and he recommended almost emptying the tank and refueling with 91 non-oxy. I usually used 87 10 ethanol. That didn't work, so I took it in and they adjusted the throttle and put new fuel filters in. That did nothing. I lost a bit of confidence there, so I took it to another shop and they test ran it with diagnostics and felt strongly it was fuel injectors. I decided to have them cleaned for a pretty penny and then took it out and it still ran the same -EXCEPT for a moment again, when I backed off the throttle it raced to 5800 rpm. It never has done that since.<br>So, I did some research and talked to another shop in Mpls and they did the following:<br>1. Ran diagnostics on dynamometer, did compression and leak down tests and inspected the VST screen and spark plugs and chamber. All returned "normal" except plugs showed rich and VST screen was dirty. So, I had them clean VST, and changed plugs and they again ran diagnostics and cited that the motor was running "in the shop tank" as it should given specs for age and output. I did not have decarbonization done since they believed the VST was the problem. I was really hopeful - but the first time out after, NO CHANGE. Actually, top rpm was 4950 and I really could not get it above 5200 rpm by backing off slightly. It still did make a small difference backing off slightly, but not as much as earlier in the season.<br>So, in a frustrated effort, I asked the shop to contact Yamaha and open a ticket. They did and I brought it back a few weeks ago. The mechanic ran it on the lake with instruments and confirmed 5000 rpm was highest he could get and I am not sure he was able or took the time to back off and find slight increase in rpm. Again, diagnostics were done in the shop were done and sent to Yamaha. Yamaha cited it was 1. Bad injectors, 2. Overweight boat, 3. Damaged hull.<br>2,3 were not the case, so I spent the $$ for new, factory injectors and IT STILL RUNS the SAME. So frustrated and completely at a loss. I reviewed the owner's manual for power loss troubleshooting and nothing there has helped. I feel given that motor is acting differently under load on the water than in the shop that has to be telling, also as this problem has developed the motor seems more "rpm stressed" by additional boat weight like trolling motors and people than before. Is there something I along with all the so-called experts are missing?
b.t.w. revving motor above 6000+ rpm in neutral is no problem. I have only done this briefly.
Any similar experiences, recommendations would really be appreciated. I have a seemingly separate issue with the lower unit and a squealing bushing I am posting on this board as well.
<br><br>Much thanks,<br>-AdamG
b.t.w. revving motor above 6000+ rpm in neutral is no problem. I have only done this briefly.
Any similar experiences, recommendations would really be appreciated. I have a seemingly separate issue with the lower unit and a squealing bushing I am posting on this board as well.
<br><br>Much thanks,<br>-AdamG
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