G3SG1 firing problem

[Gattorosso]

Hi,

thank you for hosting me here. First let me apologize for my english but I am from Italy.

I have to say it is not the first time I am disassembling and repair/upgrade the mechboxes but am now experiencing a problem I am not able to figure the solution.

Subject is a 2nd hand Marui G3 SG1 that fire with random power and accuracy, may be a shot is fine but the next 3 or 4 are weak; sometime also some BB drops from the barrel; it has been checked the hop up was set to 0.

The mechbox has been opened and checked 4 times, the gears run smoothly, the tapper plate move fine, the reverse latch spring is located as usual, the sector gear has been set up with the tapper plate knob at “hour 1” and the latch engaged (it should be another nice question why…), the air seal nozzle replaced with a new one for the correct gun, the spring is actually the standard one (tried with a M100 but the problem looked to be worse)…
The hop up has been disassembled, lubricated and riassembled.

I have no more ideas, may anybody help ?

Thanks