Campag 11 speed backpedal woes

I have a problem with a newly installed 11 speed system.

On my summer bike (short chainstays), on the biggest two sprockets, the chain is slightly fouling the sprocket below it. Now you don’t notice this in normal riding, but if you stop and backpedal to start again, the chain will move to the lower sprockets, and go slack – thus making it impossible to start again. A bummer on a steep hill. (It may happen in the 12 and 13 sprockets too, but I rarely use those. 😉 )

This is nominally a Campag set-up, but a couple of the parts are third party, which is probably the cause of the problem. The chainline is good (the BB came with the Chainset, so it should be!) so it’s not that. The rear mech adjustment is spot-on.

Has anyone else had this problem? Especially with either the chain or cassette listed below?

List of bits:

• Campagnolo Athena 11 Ergopower Levers
• Campagnolo Athena 11 short rear mech
• Campagnolo Athena 11 front mech
• FSA SL-K 10 speed 53/39 chainset
• KMC X11-L chain
• Miche Primato (Campagnolo compatible) 12-25 and 12-29 (both have problems) 11 speed cassette
• Campagnolo 11 cables