"Stiff Link?
If you have a regular, repeating skip or hitch every 3 or 4 turns of the pedals, you may have a stiff chain link. This is commonly the link where the chain was joined when it was installed. When the chain tool presses the pin through the chain, the head of the pin tends to pull the uppermost chain plate along with it, so that the two outer plates are squeezing together against the inner plates.

The easiest way to fix this is to bend the problem area of the chain into a "Z" shape, with the bad joint on the diagonal part, then flex the chain back and forth. This will slightly spread the tight plates, and free up the link. "