Yamaha F225 RPM Problem

[Edward Monoski]

I have a 2005 Yamaha F225 with 110 hours on it. When increasing the throttle at 4400 RPM it dies out. Reduce throttle back to say 4300 runs fine. I replaced the main fuel/water separator and checked the engine mounted fuel filter which was clean. Local Marine Tech said there might be a check valve in the line between the main filter and the tank which may have an object restricting flow. I can't find one. The only check valve in the system I believe is in the fuel bulb between the main filter and the engine. I have not taken that line off and check it for obstructions yet. Any suggestions?

Thanks,
Ed

 

[dale1]

Ed.

Mine did almost identical. I changed all of the filters, including the VCT. It did not help. I changed the throttle position sensor and have not had a problem since.

It was a pretty easy task. except, I had to have a tamper free hex socket for the strews. the little senor is located on top of the motor under the large cover. Starboard, rear, of the motor on top of the throttle linkage.

pretty simple. just mark your position with a scribe or marker before you remove the old sensor.

dale

 

[Edward Monoski]

Dale,

Thanks for the info on the problem. I'll give it a try but what is the VCT you mentioned?

Ed

 

[dale1]

Ed. the VCT is a small fuel filter located in the fuel system reservoir on the side of the motor. It was much more difficult to change than the throttle position sensor. I changed it first after reading about this common problem. It did not help mine. My symptoms were identical to yours.

If the throttle position sensor is not reading properly, it will not allow the motor to go past a certain RPM as a fail safe function.

Dale

 

[wspitler]

The throttle position sensor is a much less common problem than the VST (vapor separator tank) filter, but not easy to change.

 

[seasick]

The throttle position sensor is a much less common problem than the VST (vapor separator tank) filter, but not easy to change.

I agree that the VST filter is more common cause for that issue. There is a way to kind of determine if the TPS is acting up or something else.
With the motor in neutral, increase the throttle towards the point where you get the problem and see when or if the revs stop increasing. If the problem doesn't occur or occurs at a higher rev level, the TPS is probably not the culprit.
If there is a fuel flow issue, VST screen, filter etc, the motor need more fuel when under load than when not. In that case the actual load will change when the motor starts to starve and the rev point will change. When a TPS goes bad, it usually does so at a specific physical position of the sensors rotation. That position doesn't change as the load changes.

 

[dale1]

I agree, A clogged filter will usually give a slightly different set of conditions. Usually a lack of power across the RPM range. My motor would accelerate normally to 4200 or 4400 RPMs and then pull back. It felt just like running out of gas. The problem with the TPS is the intermittent condition. when mine was messing up, i could usually shut down and restart, and that would cure it. I clogged VCT will not give that scenario. At the time i did not understand the system and changed the VCT based on reading here and THT. The VCT change was not successful on mine.

After talking with a Yamaha tech he said to try the throttle position sensor, if the problem was intermittent. That makes sense now.

You would think a clogged VCT would not give an intermittent condition like a malfunctioning sensor. So, i guess it depends on what the motor is doing.

It's not a bad idea to change the filters anyway, especially with today's fuel. I'm a 20 year aircraft mechanic, and a ASE auto tech, so i always expect the worst from a stinking boat motor

Dale

 

[max366]

i had a similar intermittent problem with my F225s. Turned out to be particles in the VST and when the fuel flow increased to a point, they got sucked down and collected around the VST screen and almost shut off the fuel flow. Slow it down, the screen opened up enough to have it run right. Sometimes the white crap would not plug it off, so it showed as an intermittent problem. Changed all of the filters including the VST screen and the problem went away for good. Might be your issue as well

 

[suzukidave]

to answer the original post, the check valve in the fuel line your mechanic mentioned is an anti-syphon valve. it is a one way flow spring loaded ball valve that is installed right where the pickup tube emerges from the fuel tank. mine looks like an oversized brass npt fitting. $15 part that might be accessible from the rear deck inspection plate in the hatch where your fuel tank is located. just don't try and change it with a full fuel tank.