280 SL Won't Start and RPMs High

I've owned a '78 280SL Euromodel (I-6) for about 1 month. Got a list of about a dozen "little" things to fix. Until yesterday it was starting and running fine. Would start with first turnover of the ignition without applying gas. Now the car won't start. Just turns over and over, but the motor won't catch or even come close to catching. Is there any simple answer to this or do I need to call in the experts?! Also, the RPM's seem to run very high on this vehicle (about 4000 at 110 KPH). Why are RPM's so high? It feels like it is geared very low. Thanks for any help.