Why wont my enduro motorcycle idle steadilly?

My old Enduro dirt bike has been sitting in my garage for some time now and i finally got around to fixing it. I have it all reembled and it starts but the idle is terrible. It idles very rough. When it first starts it idols slow then it will suddenly spike up to an extremely high RPM idle to the point that i have to kill it. I have adjusted the idle on the carburetor but it always revs up very high to a dangerous level. Could it be the gas/oil mixture? or what else could it be?