Just bought a 1980 yamaha maxim and one carb was plugged but a friend bike owner was able to get it opened up. Problem now is the bike runs great on hi-way but when I stop the bike rpm levels go very high. We Used to be able to adjust the idle by turning the knob located in the middle of the bike, but now it has no affect on the rpm levels. RpmĀ“s stay same even if all the way out. Any suggestions would be greatly appreciated.