Yamaha 4-stroke 50 hp not running full rpm

[KevinDU]

I have a C-Dory 22 Cruiser with twin 2007 Yamaha 50 hp 4-strokes with almost 1000 hours on each motor. On my last trip I noticed the port engine running a bit rough around 2000 rpm, and I was unable to go full throttle. The motor just won't go past 4300 rpm. I usually run both engines around 4000 rpm which gives me 12-15 knots per hour. Anyway, the boat has been at the local Yamaha mechanic for a week now. He has soaked all injectors in Seafoam without any noticeable improvement and will check the VST (vapour separation tank) next week. There is supposed to be a filter in the VST that can clog up. If anyone has had a similar experience please let me know what the problem was. Seems like my mechanic is a bit stumped. Thanks!

[Hunkydory]

Sorry, but I can’t help with the motor problem. We run Honda 40’s. Just wanted to say, I really enjoyed your photo album. You cruise in a beautiful area. In 2004 we made it to the Khutzeymateen Grizzly Preserve, but haven’t seen the rest of the area your photos represent so well.

Jay

[tsturm]

[BrentB]

Just a guess but how old are the fuel hoses from the tank to motors.

Fuel line have outer and inner parts and the later can separate over time especially at any sharp bends like inside the rigging hose to the under the cowling fuel filter causing a fuel restriction

[KevinDU]

Thank you for all the suggestions so far!

[jennykatz]

Things to check
fuel lines how old
fuel how old
h2o seperator filter replace
injectors if they are good check also plugs
make sure all elec connections are tight coming into engine

Get a new Mechanic

[South of Heaven]

[CC Rider]

My 2006 115hp Yamaha had exactly this same symptom - would not run above 4200 RPM. I did some searching online and the most common reason was debris in the VST and specifically the small fuel screen on the entrance to the high pressure fuel pump.

The bad news was the location of the VST and integrated high pressure fuel pump - it's behind the intake manifold on the 115, which must be removed in order to get access to the VST and pump. I took it in to a Yamaha repair depot and they found that indeed, the screen/filter was partially blocked. They also wanted to sell me a new fuel pump (over $525 CDN), but I declined, so they replaced the small screen/filter and another in-line filter near the VST and I have not had a problem since.

I will probably do this service myself the next time it happens...... (need to get a shop manual for the 115.)

I know it's hard to pack everything into an outboard cowl, but you would think that the VST would be easier to access.....

Chris

[KevinDU]

[Marco Flamingo]

I'm following this since I have just one Yamaha 50. I normally don't carry a kicker, but was planning on taking my Suzuki 2.5 to Shearwater this summer. But it turns out that the Port Hardy to Shearwater BC ferry fills up way faster than I thought and I missed out. I had to settle for Kyuquot Sound this summer.

All of this gets me off topic and I will "third" that the photos in the Sea Otter album are great. I was planning on splitting my time 50/50 between the backwaters of the Great Bear Forest and the "outside" in Queen's Sound. Queen's Sound now looks like it may need 60/40. I'll have to get my reservations by April 2019.

I'll also have to look in my manual and find out what a VST is.

Mark

[jennykatz]

The VST tank and pump should not get gunk in there if you mantain your filters and watch where you fuel up NO ETHANOL gas

I hope your mechanic can fix or clean out the VST for you .Also check the fuel pickup screen and make sure there is no air sucking in pickup tube .

I had a fuel problem it was the fuel pickups sucking in air also needed to change out fuel filters water seperator and the one on engine

Good Luck

[starcrafttom]