In need of help my buddy went and replaced the gasket on the cover cylinder head side 2 which was leaking along with oil change, plugs fuel filter, and fuel petcock. when it was done I rode it home during the ride home everything seemed to work fine until I throttled down and the bike bogged down like it was not getting gas after letting off on the throttle it took awhile to even get it back up to speed and had to cruise home around 35 mph. started to trouble shoot I put the old fuel filter back on and it still did the same thing, checked the petcock and it was fine noticed when I was riding home if I put the clutch in and gave it half throttle it would rev up fine. I did read somewhere that if you overfilled the oil then it would blow by into the air filter could this cause it to bog down. I checked the sight glass and the sight glass was full up to the top completely filling the sight glass. the post I read also said to drain the oil and replace with new and fill up to the middle of the sight glass. could this cause my problem and second can I just drain some oil out instead of replacing the oil or did this cause the oil to be bad.