Gearbox problem?

[airsoftguy]

I had swapped the stock spring from my p90 with a M90 spring and installed the original spring from the p90 into my MP5 Master series. The problem is that the MP5 wont fire it will just make noise from the motor. Can anyone help?

[clayton]

that means your mp5 does not have the motor strength to spin the gears and push back the spring

[quadro]

It could be that your motor height isn't set right.