I just started noticing the bike backfires after I let it warm up a bit and the exhaust stinks with the smell of raw unburnt fuel. Sparkplug on the #2 cylinder was covered in carbon deposit and the oil was runny, and stank of gas. I know the fuel is in the oil and its parked and hasn't been ridden since, so what possible damage am I looking to have done? I only rode it about 4 blocks before the problem was recognized.