Help! My choke seems to be working backwards.

[Dugan]

New owner if a first bike, a CB77. Starts great, Runs great....when the choke is left mostly closed.

As soon as I go to open it, it revs through the roof.

So the more I open the choke, the harder is runs and If I close the choke entirely it dies at idle no matter how warm it is. Also the choke seems like it is either on or off with no I between. Still working the opposite of what I'd expect. WTF??

Also, the exhaust wrap that was white when I bought the bike, is now turning quite black.

My dad is coming to help me try and figure this out, but he hasn't worked on a motorcycle in about 40 years.

 

[Dugan]

Also, just put in new plugs...in case that matters

 

[teazer]

CB77 - great bikes. Choke on that bike is an old school plate that drops down as the lever is lifted on the left carb. Up is ON.

If it runs fast with the chokes OFF ie lever down and choke plates raised, the implication is that there's an air leak somewhere or the throttle stop screws are screwed in too far.

CB77 carbs are bolted to the head onto a 1/2" thick phenolic resin insulator block. If the two nuts are over tight the carb flange bows and allows air in. Tighten in more to stop the leak and it gets worse. Remove the carbs and clean them and while they are off replace the O rings and get the insulator blocks dead flat and also the carb flanges. Put a straightedge across the carb to see if it's bowed.