How do you clean snowmobile cylinders with aluminum piston on them?

Hydrochloric (Muriatic) Acid can be used for this. It is a mild acid,but still acid, so use care. Using an acid brush brush the acid on the aluminum, depending on the thickness of the aluminum it can that a while, but will remove all aluminum from the cylinders without causing any problems. The fumes can be rough, so ventilation is important. I have used this for years to save engines , so they can be repaired.