That happens every once in a while to me which is why I tell everyone to clean there stuff because I could be at a race and then take the kart home and the kart and motor have condensation and moisture inside the parts and stuff which is why its so important for people to completely take everything apart to clean stuff. Yes I understand this is the motor and you don't take it apart every race obviously but when at home start up for a second and then drain oil and put fresh to avoid moisture in motor and stuff. I always tape off exhaust and intake and any vents I have the moment I start loading my equipment up. But yes this happens to me a lot. Start your car up and let it run and rev it a little and then go look where the exhaust is and then there will be a condensation puddle where the exhaust exits. Mufflers like to do that a lot. Also if you are using choke and start it up it may be a little unburnt fuel but should go away after a second.