the best carb is the one that is on. go onto the dellorto web site and check out what bits you need. I changed the needle(d33), the slide(50) most common cause of poor running, the pilot jet(45) and replaced all the gaskets. then set the pilot screw to 2 and 3/4 turns out, this coupled with a new air filter(dry) helped mine to run spot on. this is cheaper than a complete new carb. all of this advice was given by Bill pye 01642 722378 and he has all the parts in stock. best of luck, mine is a cracking little bike, but i just dont have the time to ride it now.