So I have a stock beavertail 35 hp surface drive and would like to increase speed and load capacity. I have been looking into it online but can't seem to figure out what are the best options. People say to add a mikuni carb kit and aftermarket exhaust and rework the heads. What are the benefits of a single mikuni and double and would it be worth it? also i see people saying stage 1 or stage 2 what does this mean? Also what can i expect for gains when adding a mikuni and aftermarket exhaust? thanks in advance

Stage 1 ?? = heads, carb, and exhaust.
you will definitely like what it does for your motor.

Carb and exhaust, will do good also. Mikuni will get you a better idle.
But if you have a non CDI motor, advance timing key. With a CDI, advance timing key($3-$5) but not more than a #4.

premium non ethanol fuel helps, and if you can get access to aviation fuel(100 octane LL what I get).

There are lots of opinions and few options. I know some have other views, I've got a CDI Stage 1 ?? and like what it did for my motor, gained 5 mph and can run a hammer prop at 4000 rpms. Waiting on a advance timing key to see if it helps or hurts.

If you have an EFI motor even fewer options.

Wasn't thinking of that. BTW are the heads the same? If I bought a new EFI motor could I take my Heads off old motor and use them on EFI? Does the exhaust(if replaced) have to have a threaded bung whole for an O2 sensor?

Not sure about the bung, but don't think it does. Yes, the heads are the same. When they were originally released, the reps thought there was a difference, but it's only a better valve seat (it still leaks and shifts like the old ones, but is a bit better from the factory).

I like a heads, cam, and exhaust motor. It fits the needs of most people who need an extra grunt.

The only difference in the 35 heads and 37 is the valves are bigger.

^^^^^^ yeah what he said

They will still leak and show daylight around the seats after a few hours.