If the gas tank is already off or can easily be removed from the motorcycle, then use Berryman B-12 Chemtool Fuel System Cleaner (part #0116) to remove sludge and varnish buildup by swirling the product over the entire inside surface of the tank. The majority of the buildup will be on bottom, so once the sides look good, you can stick to soaking only the bottom of the tank. Depending the amount of buildup, it may take a few soaking sessions to get the bottom completely clean. If the gas tank will remain on the bike, you can use a combination of 0116 to address the bottom of the tank and Berryman B-12 Chemtool Carburetor, Choke & Throttle Body Cleaner (part #0117) to spray onto the sides of the tank. Once the gas tank is clean, you should run a premium detergent-based fuel additive like Berryman B-12 Chemtool Total Fuel System Clean-Up (part #2616) to thoroughly clean up the fuel lines, carburetor, intake valves, and combustion chambers. This will in turn help with hard starting, rough idle, and hesitation. Good luck with the bike!