I have an 81 400cm and it ran good till about a week ago. I now have to let it warm up for about 5 minutes before I can ride it or else the left cylinder will miss fire and run like crap till it gets good and warm. Also, it will run rough if I give it slow throtle after it is warm, but if I give it a hard throtle, then it runs fine. Any suggestions as to what it is and what I can do about it.