Here’s the deal with the darn motor/boat … It’ll idle/troll just fine … it’ll go on plane just fine … once on plane it starts to lose power … I can back off the throttle and then throttle it up and it’ll reach top speed (50) again only to slowly drop back down to under 20 … I put the motor into neutral and then throttle back up just fine … but no matter what I do it loses power …
The boat ran perfectly until I had a fuel fitting corrode/break off at the fuel tank … I changed the fitting, filled the tank … boat now runs like complete crap (See Above) …
I’ve changed the oil (yeah, I know - means nothing), I replaced all of the fuel line to the motor and the primer bulb, I replaced all three fuel filters, and I drained the gas tank completely and put in Ethanol free gas …
Almost sounds like its catching air some how. I’ve had other motors do that same thing and it be a bad fuel line or a loose fitting. I’m far from a mechanic but that’s my guess. good luck and keep us posted because I have the same motor.
08 210 sea hunt 150 yamaha ‘86 14’ super scout too much yamaha
I had that to happen on the same motor. My problem was the lack of oil on the fuel filter gasket. Don’t know if this could be your problem but mine was sucking air at the new filter. Hope this helps.
Sounds like the VST filter is getting clogged.It will lose rpms and you can pump the throttle to get them back up,but they will drop back in a few seconds.I had Mike Murphy @ Hanckel clean my '03 F115 and it runs fine now.
“Modern day Robin Hoodism-Steal from the sucessful and give to the poorly motivated.”
before you give up, put a piece of clear hose between the fuel line and the fuel filter under the cowling
you can then see if you have air bubles in the fuel line
I have a Yamaha 150 4stroke and my anti-siphon valve was re-stricting the fuel flow at the tank starving my engine for fuel. I installed a 3/8" hose barb (moeller brand) and now runs like new. Captain’s Choice Marine is a Yamaha service center.
