Moped Army

need some advice guys,

my 1982 chappy has started leaking gas over the last few days. i finally narrowed the source of leak to the carb.

short of changing the carb gasket (parts are hard to come by in this part of the world, Singapore), i was thinking of turning the fuel petcock off and leave the engine running tills it cuts off on its own, effectively consuming and leaving no fuel in the carb.

only thing is, the petcock on the chappy says 'on', 'pri' and 'res'.

now, i am abit confused between 'on' and 'pri'. isn't there suppose to be a 'off' too as with most other bikes? any of u fellas familiar with which is the 'off' that i am looking for?

TIA,
Josh