Regular shampoo actually works good. Make sure to seal up the carb and exhaust for the initial wash (to prevent dirt coming in)
(If you got some dirt in it it's no biggy if you disassemble everything and clean it, just don't turn it over)
Rinse in hot water, makes it easier to dry.
Lube it with WD40 to get rid of moisture
Assemble
Lube with after-run oil or ATF oil (Automatic Transmission Fluid). Be generous with it but get rid of excess oil.

Done!