A 22 mikuni will support a huge motor. You'll be fine with one of those. I doubt you'll ever build a motor too big for it. It does require you to buy an adapter (or make one), and I think they're really expensive for what they are. In my opinion, billet parts for the inside come first. Then go for an upgraded cam and valve train. You'll feel the biggest performance gains here. You can put a huge carb on a stock motor, but you'll still float your valves at 5500 RPMs. Building a motor is complicated. Some parts work well in one setup, but not as well in others. I'll suggest compiling a list of what you want. Remember, a race motor is great for racing, but not as great for just cruising. The black mamba jr. will produce a lot of power in the 2000-6000 rpm range (if I remember correctly). There are other cams that produce power from 4000 to 8000. Where will you be running the most? If you want to a of torque, and you're going to keep it under 6000 RPMs, the you won't need a 22 mikuni. If you're wanting to hit 8000 RPMs, go for the big carb and a black mamba (not the jr.) or a dyno CM cam. Without a plan, you end up buying parts that may not work with the next part you buy. Look at some of the build threads, and ask questions. Guys on here are happy to help. If you're close to Indy, jump on 70 and head east to the New Castle Motor Park some Saturday or Sunday. They do race clones there. It's mostly 2 stroke stuff, but there is a clone class. Comet Kart Sales also has guys that build motors. They may be able to guide you. If you're ever up by muncie, look me up. I'm not a builder, but I love to drink beer in the garage and play with motors.