Hmmm, your 'bent, right? Assuming that you did all the obvious things like lube the cable, tweak (or avoid) adjustment screws, etc., what else is there?
I'd look to make sure that the chain is routed properly. On 'bents this can be something of a challenge. And check the chain guide - or whatever that little wheel thing is called - for position.
These are the little things that drive a person nuts and that people like my friend Lee can diagnose before you even tell him what the problem is - over the phone.
Good luck.
Give big space to the festive dog that make sport in the roadway. Avoid entanglement with your wheel spoke.
(Sign in Japan)
1978 Raleigh Gran Prix
2003 EZ Sport AX