A tip for the Sea Foam- unhook the gas line to the carbs, drain the float bowls, and fill them with pure Sea Foam. Then tap on the carbs with the plastic handle of a screwdriver for a few minutes, to try to jar loose any crud. Then let the carbs soak for a couple of days, tap on them some more, and drain the float bowls again, then ride the bike very hard for 100 miles with half a can of Sea Foam in the gas tank, using lots of throttle in the straights. Also, the bottom of the gas tank for a bike that was parked a long time may have some old fuel in it that mixes with the better fuel added new above it.
If this does not work, try cleaning or replacing the float valves and removable jets first, then look up how to boil the carb aluminum parts to clean them, after removing all of the gaskets and other rubber and plastic parts.
I add some Sea Foam to the gas tanks of my vehicles every winter, to preserve the older fuel and to clean parts. My little lawnmower started on the first pull two days ago, with Sea Foam in the gas tank and the engine ran enough in the fall to get the Sea Foam into the carb, after changing the oil and cleaning the air filter- the spark plug was new last spring.
I also took a long break from street riding, from 1985 until 2002, then got back into the motorcycle addiction. I went from a 3.5 horsepower Briggs & Stratton to a 60cc 2-stroke to a 100cc 2-stroke to a 650cc 4-stroke (45 horsepower) to a 600cc 4-stroke with 30 stock horsepower at the back tire, bumped up a little by me later. My next bike will probably also be 600cc, but with 3 times the power and requiring higher octane fuel (Kawasaki ZZR 600).