Low maintenance/low stall clutch vs. high maintenance/high stall clutch.
Tillotson vs. Walbro carb.
KA100 has a few more hp.
KA100 seems to need less blueprinting & rebuilds.
KA100 is pipe exhaust, you can put a pipe on the KT100 but the “can” exhaust is more popular especially in sprint racing.
The KT100 does not need a lot of clutch maintenance, a quality horseman clutch with proper adjustment will do wonders for most the season. Even blue printed the engine can last a season without issue. I do not have experience with the iame KA100 but the kt100 is one of the most reliable air cooled 2 cycle engines on the market. There is good reason they been on the market longer than most engines. I personally feel they have been one of the more bullet proof 2 cycle engines ever made. The market is completely dead for them in the north east region of the U.S but they are great engines.