have you checked your jetting. sounds that your running on the lean side. i would try running the bike and getting it up to temp. and pull both plugs. the plugs should look the same for both sides. light brown at the electrode.once i get my plugs there i will raise the neddle all the way to 5 or go one or two more sizes in the main. a little wet on the plugs vs. none is always a safe zone. also i don't know what kind of rideing you do but, all i do is drag race so i run 80% water and 20% coolant. also might want to consider on getting a mega flow impeller and get ride of the plastic stock one. yes a after market head will help with flow and cool more .the cooler more hp. i would try the small easy things first before i would go buy a larger cap. radiator. good luck