G&G F2000 Semi-Auto problem after upgrade

[mrpie123]

Hi pepo of airsoft, i just got some shs 13:1 gears and took some time to re-shim and re-grease my gearbox (G&G F2000)

but anyways when im on semi auto, it shoots once and then when i pull the trigger again it doesnt shoot but if i pull the trigger the third time it shoots again and then the process carries on.

so it shoots -> doesnt shoot -> shoots -> doesnt shoot

when i was moving the piston i noticed there was a small height difference between the cylinder and the gearbox itself, is that the problem?

This is in my F2000 (just to note because f2000s, p90s seems to have problems in semi-auto)

Finally when i shoot in full auto, it shoots fine