Motorcycle Questions? Ask a Mechanic.
Hi and thank you for your question.
The problem is there is too much fluid in the crankcase of your bike. It is overfilled. Now, it could be overfilled with oil or it could be diluted with gas if the carbs have been overflowing. When the crankcase gets too full, it starts pushing the liquid through the crankcase vent and into the air box. Then it coats the paper air filter element with oil, causing the bike to run rich and foul the spark plugs, producing a very bad running bike. BTW, the oil level window is for checking the oil level with the bike upright, and engine not running, and it should have not been run in the last 5 minutes or so to assure the correct level reading.
So, you need to figure out if someone over filled the oil, or if the carbs overflowed, then replace the A?F and spark plugs. If the carbs have overflowed, evidenced by the smell of gas in the oil, the carbs will need to be gone through, cleaned and inspected to prevent a repeat.
If you have any more questions, feel free to ask.