Strange carb issue.....

[Mavrick]

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???

[teamwork000]

It is either sucking air from somewhere other than the carb bore (gaskets between card & motor). Also check your throttle cable as well by looking at the slides and how they return when you ket go of the grip. Doubt the cleaner would show anything as it is sucking, not blowing there...LOL..

[Benney]

Probably the air mixture ports are gummed up as that is what happens if they are.

Do a complete tear down of the carbs and use a good bath cleaner. Kits wouldn't hurt either if they have not been done before.

[iq180]

Just unscrew the cap off the top where the cable is and spray the slide bor with WD40, move it up and down a few times, that should fix it.

[whoknows]

Yup. Have to agree with iq180. Put the air screws back to manufacturer suggestion. Turn them in until lightly bottom and then back out a turn or what ever manufacturer suggests. Put a little liquid lube on the cables at the slides and even at the handle bars. Crank a few times without engine running and all should be good.l

[thunder bird]

Sounds more like sludge build up in the tank. Always drain your tank before you store it.
pour half a bottle of hydrogen peroxide in it, it will clear your lines. Fill your tank and
get your motor running.

[Mavrick]

Just unscrew the cap off the top where the cable is and spray the slide bor with WD40, move it up and down a few times, that should fix it.
Sticking sliders might explain the hanging idle when riding but would this also allow the bike to keep running without any mixture screws ?

[Benney]

Clean it my friend just clean it. Your carbs will love you for it.

[iq180]

Sticking sliders might explain the hanging idle when riding but would this also allow the bike to keep running without any mixture screws ?
Yes it will.