Needle in a haystack.  Kind of a wild mix of motorcycles and musical chairs.  This is a rider & passenger game normally, but I have heard of dirt bike people doing this a rider only game. 

Make a pile of hay.  A couple of bales to start should be plenty, but bigger is more fun.  Now count the number of rider passsenger teams you have and throw one less potatoe into the pile of hay.  If you have six teams then throw five potatoes into the pile of hay.  Now you will need a public address system or somebody who screams really loud.  A public address system is more fun because you can play music.  Start your teams riding in a circle around the "haystack." When the music stops the riders must stop their motorcycles and the passengers must get and scramble in the hay for a potatoe, and then remount the passenger seat with potatoe held high.

Whichever team fails to acquire a potatoe is eliminated.  Your referee gathers the potatoes and tosses them back into the haystack, and the music begins again.