Motorcycle Repair: Heavy carbon buildup, honda 650, combustion chamber

Question
Helping brother-in-law with a 1983 Honda 650 Nighthawk. It had been completely gone over about 6 yrs ago. Brother-in-law only rode it for 5-10 minute sprits up and down the street for one summer--never ran long enough to get the engine hot! then let it sit for 5 years. Removed plugs- VERY Carboned up--thru them out. Oiled cylinders and turned engine by hand it did break free and turn but looking in the cylinders I see heavy carbon buildup on the pistons so I guess it is everywhere. Removed and cleaned the carbs. Is there anything we can run thru the engine to remove the carb buildup? I really do not want to pull the heads if I do not have to. We have not tried to start it yet--will be putting the carbs back on tomorrow. Thanks. Joe

Answer
Joe,
get the engine running and warmed up,
then get a spray bottle and fill it with water.
Let the engine idle and slowly spray water into
the carbs intake or air cleaner housing .
Don't speed engine up too much or add too
much water as it doesn't compress and could
damage the engine. Just keep spraying until
you use most of the bottle up.
The water will turn to steam and when it hits
the hot carbon it breaks it down and will
clean out the combustion chamber and piston.
There may be alot of white smoke which is usual.