Best carbs out there imo. My bro runs one on his yfz, he loves it, sold me on it! I plan on putting dual 36's when I get ported this winter. As for tuning- its the easiest carb you will ever tune. As for sizes- I'm not sure all of the sizes they make, check out http://www.packardracing.com you can post up, or call Dennis. He knows his stuff, and is a great guy to deal with.