Horse Power cost money!!!!!
Run the biggest motor you can run in that class. Check out the Killer Kohler build up in this site:
http://kirkengines.com/
The motor in my 100 has the same mods done to it that David Kirk did to his 1250. It did make a big difference to the motor. I would stay away from the 18 horse power cam. I use to have one in a K321 block. You can make better power from Kirk's cheater cam. I would check with Vogel, Midwest Super Cub and Lakota to see what cams they offer.
To get 30 horse power you will need to go to alcohol and the biggest motor allowed in the class. Alcohol can be pain to use if you don't know what you are doing. Best thing you can do is run on gas and get use to a modified motor first. Trying to run too big of a carb with hurt performace. I would check the class rules first to see what size bore in the carb they allow. That could help to deside what carb to run.
If you having mega horse power you will need to beef up the clutch, driveshaft and trans/rear end. Selecting the right tires and gearing is a must too. The biggest factor is getting the weight balance set right.
Start out in a stock/run what you got type class. The first thing you need to learn is proper balance.