Exhaust by pass

[jamie berry]

My older 1989 Yamaha 9.9 4 stroke (high thrust) sits a bit lower in the water than recommended. The engine is used as an auxiliary on a 33 foot trimaran sailboat. As a result, the exhaust back pressure is high. This makes the engine idle a bit spotty. To lower the back pressure, I would like to enlarge the diameter of the exhaust by pass hole. The plan is to run a drill bit of a larger diameter up the by pass channel. I worry that this might compromise the walls that probably surround the engine oil reservoir. The local dealer was not sure . Any suggetions?

Jamie Berry Belliville ON Canada

 

[rodbolt]

Re: Exhaust by pass

simply raise the motor a few inches. DO NOT try to drill it.