advise on tuning rear deraileur

Hi to All,

I would like to hear some advise and opinion.

I have been to some bumpy terrain and now face a little problem with the rear deraileur.
I have a dahon P24 and a flamingo F1, both have this problem.

I can feel that the deraileur is shifting my itself without my input.
I've went back to the shop where i purchase the bike and they have briefly tune it (on dahon, flamingo not yet)
short distance is alright but still have this fault after cycling longer distances.
After tune, i observe strange feel on the crankarm and pedal....
it's goes like, when you idle the pedal for cruising for a while and when you decided to pedal again, there is a "slipping" feel before you start to cycle.
quite difficult to explain but hope some guys know what i'm saying here.

Now thinking of going to other shop to tune it and with reasonable charge.

Thanks in advance....

WeeLee

The "slipping" feel is not caused by your rear d, rather is caused by your rear hub if i'm not wrong... i have same issue with my mountain bike years ago using XTR hub, no amount of tuning can solve the problem, in the end i settled for a Chris King ISO hub and that weird "slipping" was gone.