1999 honda foreman 450es oil change

[99_300ex]

hi everyone i just bought a 1999 honda foreman 450 and was wanting to change the oil so i was wondering what the best weight to use is and how much. one other thing is that every once in awhile it will backfire on deceleration i have ran almost a full tank of gas through it and put some carb cleaner in it i wondered if it was maybe a tight valve or something so if anyone has some insight on it help would be greatly appreciated thanks!!!

[Colby@C&DRacing]

the engine oil will be a 10w40 should take around 2.4 qts. The backfire on decel could be a lean jetting sympton.