I'm new to these bikes and I'm not sure what is normal. I have a 1986 Vmax and I have noticed that when idling if I crack the throttle and also on acceleration that I can hear a fairly faint popping what seems to be coming from under the air box. I'm wondering if it's an intake valve issue. If so, how much $$$ should I expect to pay for a valve job on that head. Also does the motor have to come out of the frame to do that?