I'm no expert, but I'll chime in with some suggestions...
If you haven't done so already, I'd start by taking it down and thoroughly cleaning it. There could be enough grit or filings to cause some resistance for the bolt carrier or piston.
Try different ammo. Probably not the cause, but if it is, it's the easiest component to replace.
This THR thread has some good tips for inspecting for flaws. Some of them (weak recoil spring, or imperfections which require filing) are fairly easy to fix. Others (misaligned gas port) may require a trip to the gunsmith.
You could try adding a recoil buffer. I don't think they're necessary in most cases, but I've read of them being used to help with improperly-cut upper rails... it doesn't sound like that's your problem (unless the bolt carrier is getting jammed up to the rear end of its travel) but it's a fairly cheap test.
I hate to even mention it, but the only major FTF problem I've personally seen in an AKM was the result of a poorly-assembled kit build. My buddy had welded his rails on too low in the receiver and had constant feeding and cycling problems. In his case, he had to drill out the rails and mount a new set. If yours is a commercially-built WASR, I'm guessing this probably isn't the case, but it's worth mentioning in case yours happens to be a home-built Romy sold as a WASR.