Yamaha 8A carb change or porting

Hello, i have an old engine laying around, the Yamaha 8A (8 HP 2 cilinder)
I like 2 stroke and i want to make it faster.

This is my plan:

1. Put a other carb on it to make it faster, but i cant find information with carb works on my engine, maybe from a go kart..

2. If a other carb isnt a option, than i want to port the engine my selve, does any one have pictures from a small block outboard, than i can look at it how to do it the right way.

I want to make it faster and i like to work on a engine, but what is the best way to make it faster?
If you guys need pictures, i will post them!

btw I have tuned a engine before, here a video...
https://www.youtube.com/watch?v=1acAEpz6Lzc

Greets Jelte!

I "think" the 8 and 9.9 were the same engine for a while. Minor differences.

Might be worth a look at a parts diagram to pick out which parts are different. That should give you an idea which direction to go. perhaps your 8 could be turned into a 15 if the homework is done right.

I use to have a yamaha 6hp and changed it to a 8hp by changing the carb. The 6&8hp we basically the same motors just with diffrent carbs. Honestly it woukd be easier and cheaper to just sell it and buy a 9.9 or 15hp than it would to try and modify it.

If you do go through with spending the money and modding it make sure you check out the difference in exhaust cans and porting.

If you just do carbs you may end up with a crap running 8 h.p. instead of what you want.

Increase in displacement is the way to go.

Working an outboard to increase horsepower by increasing rpm's is expensive. Life of the modified outboard engine will also be seriously compromised. Another thing is you will need to use a non TCW3 oil and high octane fuel.

My advice is sell the 8 horse and buy a 9.9 or 15. That is if your boat is rated to handle 9.9 or 15 horse power. If your currant boat is not rated to handle 9.9 or 15 than you have two options.

Keep it and enjoy what you have. The 8 hp Yamaha outboard is one reliable engine.
Or
Sell the boat and motor and move up to a boat that can handle the extra hp.

Another thing is modifying an outboard as what your describing will take more than porting and carb.

You will need to work all below:

Compression, timing, porting, carburetor, reeds, exhaust and possibly ignition. That is if the igniting has a built in rev limiter.

These engines are not built like the old Suzuki RM and Yamaha YZ motocross race engines from the 70's and 80's. Back than cylinders were easy to port, compression was easy to increase. I been through all this for years, I had a 1975 Suzuki RM 125 that would smoke everyone on the straights. But if the rpm's were not kept up over 8000 rpm's the engine would lose all torque and bog down. The other thing is the engine needed to be re-ringed every third race.

Another important thing to check out is I believe it is illegal to modify an outboard built after 1998.