Topic: 1981 CB650 C rejetting questions

[Samgo]

Hey yinz,
Working on a 1981 cb650 c with a 4 into one exhaust. It has a Stock airbox in pretty good condition. Boots are all supple and there are no cracks anywhere. The carbs on this bike are the keihin vb44c which come off of the cb650 sc. I changed the main jets to 120 (stock is 118). It Seems to idle pretty well, drops back down to idle really quick once you let off throttle. I Adjusted the air mixture screws to 2 1/4 out. When I get on the bike and rip down the road it stumbles and stutters around 4500 to 6000 but once its past this it rips and runs clean and has great response. If you crack the throttle open as fast as you can  from idle it hesitates and eventually opens up.
Any suggestions or help is much appreciated.
 

[fizzlebottom]

If you have a stumble from idle when you crack the throttle, you may have a gummed up accelerator pump circuit or a ripped diaphragm. The carbs may not be in sync either, and these things are stupid finnicky with how in sync they need to be.

Your other issue is likely happening because of your jetting. You should not need to change jetting with that exhaust. Put the original mains back in and see how things change. If you have the original Keihin brass, use that.