300,000 wt. diff oil?? That'd be like filling that thing with frozen peanut butter! I'm assuming you meant 30,000 wt. (Or maybe it really is 300,000) LOL

Anywho... have you checked to see if your engine sucked any crud into it while the airfilter was off? I'd be tempted to pull the engine apart and give it a good cleaning and inspection before starting it again.