So I pulled my 1982 CB450SC Nighthawk out from storage and noticed something strange while riding it for the first time this year. It started great, choke worked fine, but while riding it when I went to down-shift the revs stayed high (around 3000 RPM), with the clutch pulled and my hand completely off the throttle it stayed revving high for at least 15 seconds every time I went to downshift. So I got it back home and thought maybe the carbs might need to by synced so I pulled out the vacuum gauges. After hooking them up and starting the bike I started adjusting the mixture screws and noticed no change in RPM's no matter what I did to the mixture screws, I turned them all the way in (seated) and no change to the RPM's, so tried something crazy and unscrewed them all the way out (yes both mixture screws completely removed) and the bike continued to run with no change to the RPM's. Even sprayed carb-cleaner around all the boots looking for a vacuum leak but found none. So can someone please tell me how the heck a bike can run with no mixture screws installed, I can't for the life of me figure out what's wrong and I'm about to take a sledge-hammer to this thing…..any ideas???
