Ive used "tec" top engine cleaner from gm with great results!!
Just follow the directions, and it will clean out the top end well and everthing else. When I use it I warm up the engine 20 mins, and pour it down the carb slowly 1st and then choke out the motor when you dump the rest in. I let it sit overnight and in the morning
I fire it up and blast
it down the road @ 10 mins or when the smoking stops. And then you better change the oil and filter, because all the "tec" washes the rings and walls of the clys, and heads south into the oil pan. Then take it for another normal ride
