Engine boggs down at 3000 rpm

[RGeddesNC]

I have a 2001 Yahama 115 4 stroke engine. The last few times that I took the boat out it works fine for about an hour. When we are at throttle. I went thru a no wake zone and slowed down. When I tried to speed back up, it bogged down at 3000 rpm. It would work fine up to that point. I've had two boat mechanics look at it. The first one replaced the fuel injectors and cleaned the VST. It worked for one trip, then started again. The second mechanic said the engine was not heating up due to a stuck thermostat. This worked for a few trips, then started again today. What is curious is that it works fine for 30 minutes to an hour before this issue starts. Any advice on where to go from here?

 

[abirdwell]

I have a 2001 Yahama 115 4 stroke engine. The last few times that I took the boat out it works fine for about an hour. When we are at throttle. I went thru a no wake zone and slowed down. When I tried to speed back up, it bogged down at 3000 rpm. It would work fine up to that point. I've had two boat mechanics look at it. The first one replaced the fuel injectors and cleaned the VST. It worked for one trip, then started again. The second mechanic said the engine was not heating up due to a stuck thermostat. This worked for a few trips, then started again today. What is curious is that it works fine for 30 minutes to an hour before this issue starts. Any advice on where to go from here?

Do you notice a difference depending on the temperature outside? How is the oil? Does it smell gassy at all? Could be the low pressure pump. This is assuming your fuel/water sep and inline fuel filters are changed and no water was present.

 

[RGeddesNC]

Fuel/water sep was just replaced along with the fuel filter. Temperature does not make a difference. Oil looks clean. It runs fine at throttle 4K -5k rpm’s. Once you stop or slow down, it won’t throttle up past 3k rpm’s.

 

[KJM]

Wouldn't be something simple like a blocked vent in the gas tank creating a vacuum? At one time I had a somewhat similar problem that just turned out to be a kinked flexible gas line! Hopefully you'll get lucky and it will be a similar fix.

 

[RGeddesNC]

Wouldn't be something simple like a blocked vent in the gas tank creating a vacuum? At one time I had a somewhat similar problem that just turned out to be a kinked flexible gas line! Hopefully you'll get lucky and it will be a similar fix.

That’s a good point. I had an issue with the gas vent. It broke off while docking. It was quickly replaced to get back going. The issue started after the gas vent broke. Let me check that.

 

[RGeddesNC]

Replacing the gas vent helped a little. The engine is not going into limp mode. Now, it will boggs down at 3,500 rpms, I can back it off and get it back up to 4,500 rpms, but that's the top. I am going to check the VST. Based on this new information, the VST may be clogged again.