I own, and have owned a few of these Honda singles.
Been down the "make it less slow" and all that before. Personally I now just prefer them stock. I view them as best in this role.
BUT completely understand the desire to learn and just generally make something out of random parts. In that respect these bikes are great for that.
They are small, parts are easy to get and cheap. Honda made millions of these things. I would rather see someone learn to mix and match junk on one of these then blow apart a 4 cylinder and drown.
The idea should always be fun.
But dont brush off what people are saying by using the cop out " ill learn it myself". If that was the case then you would not be on the internet seeking out help, you would be in the garage doing something. So take some advice and you will have a leg up.
That motor that kerosene was talking about might be something fun for you to build.
What I would do is service the shit out of the bike you have and ride the wheels off it. While doing that find a spare motor and build it up.
You will then be wrenching on a fun project AND riding the bike. Then one weekend swap the motors. Another thing you gain with this is a good baseline.
the 18hp of the new motor will still feel slow, unless you have been riding around for a while with 11hp.....
And we do still need to talk about how bad these bikes are at "cafe racer" builds.
The motors HATE to run with short pipes or pods. Rearsets are hard to mount. ect ect
Play to a bikes strengths. "racing" aint it.
Here is mine
Bought it with 1100 miles from the original owner's family. I use it to run out for beer (that rack is epic), pick up parts and just general running around.
It is a blast. Have run it out on the beach, and taken it though the woods. Just a nice bike to have around.