1987 Rx7 recently purchased and havn't gone through whole motor yet, what are some reasons for there being gas in my oil.

I know it could be a bad injector, but how could I tell which injector is bad?

 

What makes you think there is gas in the oil?

If you are seeing a white, milky goo in the oil filler neck and cap, that is condensation and typically happens this time of year.

If you are smelling it, then it could just be the oil has been there too long. Fuel dilution in rotaries is pretty common. These cars really can't do long oil change intervals as a result.