If you are talking about the 9.5 "pancake" fishing engine then changing carbs is not an option. It was a special mount and special carb for that engine.
As far as timing you need to understand a couple of things: 1. Most crossflow engines use approximately 30 degrees advance at WOT. This is because gasoline has a definite burn rate (it is not an explosion). To develop maximum power the TIME of burning before and after top dead center must be equal. Excess timing advance actually decreases power and causes engine damage, 2. Loop charged engines usually use about 18 degrees timing advance. This is because the combustion chamber design causes more turbulence and faster burning. Thus less timing advance is needed. Because of this and other factors, all other things being equal, a loop charged engine will produce more horsepower than a crossflow. 3. Usually, horsepower is set by the factory by port timing. Two equal displacement engines with different porting and the same carb will produce different horsepowers. Putting on a bigger carb will increase horsepower a little, but not to the degree you would like. It is similar to an auto where adding a 4 barrel carb will add a little horsepower but unless you change the cam, heads, and manifold to take advantage of the additional airflow capacity of the carb, you simply won't see remarkable results.
