Look carefully for a kink in the cable, #### through the gears to see if you can spot one. Any binding at any location where the cable goes in and out of the housing could cause this. Also check the B tension screw adjustment. Refer to the internet for what it should look like. Lots of info on how to set it up.
If your last resort is to take it to a shop, you may as well look online on how to tune a derailleur, maybe you can fix it, and if not, it was already messed up. Once you learn a few tricks, it's not a hard job, and will save you being out a bike when it goes bad!
|