Failed aircare with high CO
 

I'm a newbie to this forum, and a newbie to mazda trucks in general! Just picked up a b2200 (1988) king cab ... it has a rebuilt engine and runs very smoothly. However, it failed aircare (for those who don't know what that is, it's an emissons test vehicles need to go through every year here in BC).

The readings were very high Carbon Monixide (CO) and also Hydrocarbons just over the limit. Now before I take it to a mechanic to diagnose, are there any obvious (or common) things that my truck would need replacing in this case? I'm thinking the oxygen sensor could be the ticket.

Are there common vaccuum leaks as well?