2002 Tohatsu M40D2 Engine performance issues

I purchased a nice boat with a M40D2 three cylinder outboard. When I first took it out it ran fine but than seemed to drop to 2 cylinders(At least that is how it feels). I came home, checked the plugs and found the bottom plug wet while the other two were grey(as they should be). Changed plugs and it seemed to work fine. Ran at least 18 miles with no problem. Next time out the same problem re-occured. This time the portable gas tank seemed to be sucked in. Tank has no separate air vent. Next time out everything ok again. This last time out it seemed to drop to one cylinder, but at least it kept running to get me back in. I can't figure out what is going on. Would appreciate some ideas. I think it must be gas flow related but don't know.

Re: 2002 Tohatsu M40D2 Engine performance issues

You have to always have proper ventilation at the tank ....

Re: 2002 Tohatsu M40D2 Engine performance issues

Yep. If that's a plastic tank, there must be a vent that needs to be open when running. Some older non-Tohatsu metal tanks had integral venting, but most of those have rusted and been taken out of service.