Reeds and the silencer packing will slow response off bottom. A plugged air filter of course also. Them stupid cd manuals, most are nothing more than parts micro fiches, hate them. A clymers would be way better, and of course the oem shop manual. Even the owners manual should cover the carb. There is a site for yamaha manuals free. The float valve is a high wear item, replace it yearly. Clean the carb thoroughly, actually poking something completely through the passages and jets. Floats do not go out of adjustment by their selves. They need help, except for leaking. Some carbs have a tube coming out of the bowl, it can hit the floats if one is not careful. Or someone has fuel puking, the first thing they do is fiddle with the float. You can not just look at, or push the float up and watch the gas ebb, and say they are good to go. Maybe with a strong magnifier and good light, no, just replace the float valve and seat! Performing a leak down test is real important for bikes that pass the float valve. As long as you have good top and bottom end sealing, then its all in the carb jetting. Used carbs, look very carefully at the slide needle and seat, as the 3 rubber connectors to the carb. The jetting guide in post #2 is fairly accurate, and eaasy to follow. An online parts micro fiche will tell you the stock jetting specs, some state it, and some just list it first: NEEDLE STD
275-14116-J1-00 , JET,PILOT(#35) STD
4KM-14142-35-00 ,. What does your air screw setting at 1 1/2 tell you?