Mod C was racing in the early 1990’s. It was a tunnel Class with Mod motors up to 35 cubic inch. The favorite motor was the 30 hp Yamaha triple. That motor was 31 cubic inches. The modifications were extreme....custom sleeves, and Pistons to increase the displacement to 35 cubic inch...special reed cages, crankshaft work, larger carburetors, exhaust, nose cone gearcases etc....a lot of money!
Since then many found that just a few simple mods really increases the performance and really didn’t change the original running characteristics of the stock 30 hp.
Here is an example of one.
https://www.youtube.com/shorts/9c7AWT7CGp8The first thing you notice is the larger carburetors. This motor has Tohatsu 40 hp carburetors. Like the stock 30 Yamaha the fuel pump is on a carburetor so they are an ideal replacement on a manual start 30 hp. The jetting in the 40 carburetors is OK as is for the 30 Yamaha. You enlarge the intake opening to match and install 40 hp Yamaha reed cages. A couple of thousand off the cylinder head will jump the compression to about 150 lbs. Most clean up the ports, weld the crank but leave the exhaust stock. The increase is 10 to 14 horsepower and more rpm at the top end on a light boat.
Tohatsu carburetors are pricey and rare. The 40 Yamaha carburetors are easy to find. They don’t have the fuel pump carburetor mounting, but if your 30 is electric start. I would run those carbs with a small electric fuel pump. If the motor is oil injection I would remove the OI system, remove the the choke butterflies from the carbs, install an primer choke and run the choke fuel lines to the oil injection intakes on the intake manifold.
I also would switch gearcases and run a 40/50 hp Yamaha gearcase which allows you to run a wider selection of performance props.
For those of us that appreciate the STOCK 30 hp Yamaha triple. This just makes it that much better.
