CYMA P90 not feeding/firing
 

I recently bought a CYMA P90, which was working out of the box. After I changed the spring for a Modify S90 to lower the FPS, the gun will either not fire, or fire 1 bb every 10 or so shots that goes about 20 feet then drops. The gearbox works when out of the gun (I can feel it pushing out air) so I don't think it's a compression issue.

My guess is that it's something to do with the hop up unit/inner barrel, but I don't have any spare parts to check that.

UPDATE: I got it working. The issue was that the air nozzle was not seated on the groove on the tappet plate, so a proper seal between the hop up and the gearbox was not created when the trigger was fired (it was seated before when I incorrectly put the gearbox together)

Hop up unit on p90 breaks easily... Check for any breakage.

Make sure you push it in all the way. Screws/ shim/plate in the butt stock in place?

The hop up unit that comes stock looks like really cheap plastic, so I wouldn't be surprised if that was what broke. The plate in the butt stock is in place, I made sure the screws were actually screwing in.

did you reinstall the tappet plate spring?

I got it working. The issue was that the air nozzle was not seated on the groove on the tappet plate, so a proper seal between the hop up and the gearbox was not created when the trigger was fired (it was seated before when I incorrectly put the gearbox together)