50 hp Johnson 2 stroke wont go above 10 mph

[mbecks21]

My folks bought a used pontoon a few months ago. 20' weeres with a 2000 Johnson 50hp 2 stroke. Ran great for about a month. Then we noticed it was losing power. It will not open up at WOT. Just putts along at about 8-10 mph. About the same time we noticed a leaking gas tank. 12 gallon tank. Pre-mix since the oil injector was removed by the previous owner. We fixed the leak but the throttle problem still persists. When idling, sometimes it idles fine and other times it idles rough and stalls. The primer bulb seems to be emptying more than it should. Any suggestions would be appreciated. Thanks

 

[Tim Frank]

Can you describe the gas leak more clearly and how you "fixed' it?

 

[mbecks21]

My brother replaced the fitting from the gas line to the tank. I did see some gas on the top of the tank yesterday so maybe there still is a leak. Could this be the problem? This tank has a vent on the gas cap. I am not too familiar with this setup. Could it still be getting too much air? The gas tank must be vented when operating correct? Every time I unscrew the gas cap it releases a lot of pressure. Is this normal? When idling I can rev it in neutral with no problems. But once in gear, the rpms dont get very high. BTW this boat has no tach.

 

[fireman57]

If it is releasing pressure then it is not vented and you are "running out of gas" Try loosening the cap and see if the problem goes away.

 

[Silvertip]

Has anyone removed the plugs to see if the engine is running on only one cylinder? And yes -- the tank must be vented during operation. If the primer bulb is emptying as you say (as in being sucked flat or partially flat) then that's an indication of a non-vented tank. Suck hard on an empty soda bottle and notice how the sides cave in. Basic physics 101.