3.0 power loss

[Steve Chasteen]

I have a 2015 175 Bayliner with Mercruiser 3.0. It will run just As it should, but an hour in it will lose power at high speed. Runs well at idle and low speed. Replaced the fuel pump, drained the Tank through the supply line to engine. This convinced me that the tank had no water, the check valve was working and the line filter was not clogged. What else should I look at before I got into the cab. It has the TDK? Carb! Runs great and then goes down hill fast. Still runs but no real power. All help is appreciated!

 

[itsathepete]

Check your fuel tank vent and anti siphon valve.

 

[Steve Chasteen]

I will recheck the tank vent, but where is the antisiphon valve?
Thanks Steve

 

[alldodge]

TKS carb
The antisiphon valve is connected to the top of tank and has a barbed fitting which the rubber fuel line connects that goes to the fuel filter/pump

If you can start and it runs fine at first even at high speeds and then starts loosing power over some time. Can shut it down for a while and then can do it all over again, its probably the tank vent

If it stays at low power from the get go, then look at the antisiphon valve, filter and fuel pump

 

[Steve Chasteen]

Is it the same as the check valve coming out of the tank and going directly into the line to the fuel pump?
Steve

 

[alldodge]

Is it the same as the check valve coming out of the tank and going directly into the line to the fuel pump?
Steve

Yes

 

[Steve Chasteen]

I put a small hand transfer pump on the fitting and used it to drain the tank. It took very little effort. So the valve could work as designed and fail to work at times? Next time it happens I will park the boat for an hour and if it then works it is probably the check valve? Correct? Then the question is how to get the check valve off the fitting without snapping it. Buy a boat they said, “It will be fun”

Steve

 

[alldodge]

If it takes a while before it happens its not the valve

When it happens, stop the motor. Go to the gas cap and get your ear close to the gas cap, then open the cap. If you hear air suck in then its the tank vent line, might be clogged

 

[Steve Chasteen]

Thanks for the help. I will give it a try over the next few days and post what I find.
Steve