Sorry to hear you already bought a centrifugal clutch. Try to return it. The problem with the clutch is it is either engaged completely, or it isn't. There's not much middle ground, slippage. Thats when they get red hot and fail. A torque converter is a complete transmission. It can be driven at any throttle setting. The 30 series is much more popular than the 20, and will work well enough. You can find them
( the complete system ) on Amazon for about $70. You will not get a better one by spending more money. They are all made in China and are all the same. I have five of them. One on everything I own. Do like Denny suggest, and read up on them. They are not hard to understand, and are easy to install. They start out in a lower gear ( and will stay there all day if you want ) and shift to a higher gear as more throttle is applied. Just like your car.