Motorcycle Repair: cb450 1970, air mixture, rubber boots

Question
Hi I own a honda 1970 cb450. I hope you can help me with a question. I see you  are best with later bikes but I figure you might have a idea. This bike rides great but recently while at idle position at 1000 rpm it increases to 4000 rms without any reason. I rebuilt both carbs and even disconnected the throddle cable yet the bike just increase in rpms. The rmps will go down once I engage  the clutch but will increase rmps in a few moments. any idea whats going on. thanks so much

Answer
I would check the rubber boots between the carbs and the head.  They should be soft and pliable, and have no cracks.  Otherwise it does sound like you need to clean the carbs again, and make sure the idle air mixture screws are set correctly.

Good luck,  Jan