i have problem with ma mc21
when i start bike one cylinder doesn't work (up cylinder always)i have to change new spark plug and it works,bike goes well,but after short time it stops working or next day when i start bike again same problem bike starts with one cylinder and upper cylinder dont work so if i going to ride bike i have to put new plug evry time so what it can be,what can foul plug same cylinder always???
(bike is 100%stock)
did anyone had same problem???please help!!!