Is it safe to close upper exhaust holes?

Hello all,

I have an 8 HP Yamaha two-stroke outboard engine from the late 90s. It is mounted in the engine well of my old Hallberg Rassy Misil sailing yacht.



However, if I close the hatch of the engine well while the engine is running, a lot of exhaust smoke builds up, and the engine starts to choke.

The main exhaust outlet is in the propeller, but I have found two other small outlets above the waterline, which are the source of the smoke in the engine well.



After a bit of googling, I have found out that the outlets are used to make sure that exhaust can easily escape, even if the engine is idling or in reverse.

I've tried to close the holes with my fingers while the engine is idling, and it continues to run smoothly. The only difference is, that the exhaust starts bubbling from the propeller instead of coming out of the two small holes.

My question is now: Can I safely close the two exhaust holes? Could it harm the engine or could it harm its performance? And if I were to close the holes, how would I do it? Glue? Exhaust Paste (Gun Gum)?

Thanks a lot for your help!

Greetings from Copenhagen, Denmark

Mikkel

Re: Is it safe to close upper exhaust holes?

Before I plugged them I would consider trying to reroute them somehow. I would think they are there for a reason.