'96 evinrude 9.9 2 stroke running rough

[markatmfasis]

I just purchased a boat that came with a '96 evinrude 9.9 2 stroke. It is a sailboat so this motor doesnt get much use. It ran very well for a month or so. 2 weeks ago I had it running at high rpm for about 20 min when the rpms suddenly dropped. It would run at idle out of gear no problem. But when I put it in gear I could only slowly increase the throttle or it would stall. I made it back to mooring and realized that I had not opened the vent on the gas tank after filling it last.<br /><br />The following weekend it seemed to run fine. This past weekend, however, it started doing the same thing. I checked the fuel line and everthing seems fine. The filter is clear. I drained the carb bowl thinking that there might be water in it. I then found that if I pulled the choke lever about half way the motor ran perfectly. <br /><br />I am at a loss. Any words of wisdom?<br /><br />Mark

 

[Xcusme]

Re: '96 evinrude 9.9 2 stroke running rough

Mark, Welcome to iboats.!<br /><br />Running better with the choke partially engaged, usually points to a fuel delivery problem. If pumping the primer bulb does not improve the running issue, it probably time for a carb cleaning-rebuild. Carb rebuild kits are cheap, and with the help from a service manual, and easy task to install. If pumping the primer bulb does improve the idle-running, then this points to the fuel pump. As you have already figured out, the tank vent must be open, otherwise, the fuel pump can't draw fuel from the tank ( draws a vacuum from the tank).