boat lags in full throtle

[hbah923]

I have a 1989 50hp force. The title says 1989 but the serial number indicates 1988. It is on a 24' heavy pontoon boat. When I take off from idle and go full throtle the engine lags until the boat starts to get a little speed and then the motor will go full throtle. Sometimes the engine will die while it is lagging if it takes to long to get the speed going. The carb was adjusted. I tried pumping the bulb on the fuel line. Nothing helps. One person told me i need a torque prop and not a speed prop. If this is the case what size prop do i need (what pitch). One more thing. when the motor is idling the motor will have a knock ever once in a while but not when it is open throtle. Any help whould be great.

 

[justin65]

Re: boat lags in full throtle

Sounds like its working hard to get the boat moving.
Could the motor be too small?

My brother-in-law has a Merc 90hp on his 24' "party barge" pontoon boat but its rated for a 120hp.

 

[Frank Acampora]

Re: boat lags in full throtle

Every time I hear "the carb was adjusted", I begin to worry. Who did it? a friend, or a mechanic that knows these engines?

Typically, if the engine is running too lean, upon full throttle, it will attempt to die, or indeed die , then recover and run well as speed increases. Lean running melts pistons. If this is the case, do not let it continue. The low speed adjusting needle should be no less than 3/4 turns out from lightly seated, preferably 7/8 no matter how rough the idle is.

For normal all around use, that engine would take someplace around a 10 3/8 diameter X 13 inch pitch three blade prop. For something as heavy as your boat you would need to drop down at least two pitches. Go over to prop forum. They have a lot of very knowledgeable guys there who will steer you correctly--they also know what is available for your engine

 

[WillyBWright]

Re: boat lags in full throtle

To set idle mixture properly, the motor has to be in the water and warm. In general, set for smooth idle and open it up another quarter turn or so. Someplace in the ballpark of one full turn is where it will end up. If you set it for smoothest idle, it'll bog and die on acceleration every time.