The Boating Forum - Help Me Troubleshoot Problem with my 2000 Yamaha 90

I have a 2000 Yamaha 90 2-stroke that started giving me problems today. While running at about 4500 rpm, the engine bogged down and backed off to 2000 rpm. No alarms sounded (oil or overheat). My oil level indicator was down 1 bar, so my first thought was that the oil was low (looked at the tank and it was low) and that my RPMs were automatically being limited. Added some more oil and it still acted the same. My next thought was that it was a fuel restriction issue, but that doesn't seem to be the case because when I rev the engine (not in gear), it will rev up to 5000 rpm, so it seems like it's getting gas. When I push the throttle forward to try to plane off, it gets up to about 2200-2300 pm and then backs off the exactly 2000 rpm every time. I limped back in and haven't had time to mess with it at all, but just wondering if anyone has any suggestions. My first thoughts will be to check fuel filter in the engine and the Racor and check the plugs for fouling as well. Only about 50 hours on the engine since the last 100 hr service. I'm hoping it's not an ethanol related issue - I use StarTron religiously. Please let me know if you have any thoughts on this. Thanks.

Check your tank vent. IF your tank vent has a restriction then it will act like that. Open the cap on the fuel tank and try getting on plane. If it does fine then it is your vent.

Get a 6 gallon tank and hook it up to your engine. Go run the boat. If it still messes up then you know it is on the engine and not on the fuel system.

This may sound redundent but you have to isolate the problem from boat problem to engine problem.

Do that and report back to us.

If it runs fine I would probably replace the fuel pumps. Depending on what model engine you have it is pretty easy and economical to change.

Good luck.

Are you sure the overheat alarm is hooked up and working? Those 3 cyl Yamahas will have water passage restriction from salt residue. If you don't use salt away those passages can restrict and put the motor in limp mode. Make sure you have checked for that...good luck!

Thanks for the suggestions so far.

Matt, I will check the tank vent and try hooking up a remote tank.

The overheat alarm was working fine last winter - my water pump needed to be replaced and the engine kept overheating - just had the water pump replaced about 25 hours ago, and it is shooting out water just fine. We stopped and fished for an hour and let it cool down, and the problem persisted, so I don't think it's an overheat.

The weird thing to me is that it limits me to exactly 2000 rpm - seems to me that the engine is automatically trying to limit my rpms for some reason. But then again, I can rev the engine up to 5000 rpm with no problem.

Keep the suggestions coming, I would love to be able to get this straightened out myself without having to take the boat in to the mechanic.

Talked to my mechanic today, he seemed to think there was more to it than a fuel restriction issue and said the engine was probably locked in safety mode since it was limiting me to 2000 rpm. Said it could be oil injection issue, oil sensor, power pack, etc. Not exactly what I wanted to hear. Any other ideas?

Keep us posted with the results. I just took ownership of a 2002 Yam 90...