gearboxes (springs)

I just bought a new G&G m4A1 combat machine w/ high torque motor. it has a little bit lower fps than i want (it is currently 380...according to multiple sites and comments.) and was thinking about upgrading the spring.
First, what spring would you guys recommend for this gun
Second, I've heard taking apart and reassembling gearboxes and their parts can be tough and I was wondering if you guys had any idea of how to do it without totally messing everything up in the gearbox and prevent me from buying a whole new one....

To be honest with you right now , I would leave the FPS along, 380 FPS is good enough. Second if your not familiar with gearboxes chances are something will go wrong and you'll be out of an new AEG, also at the Hotel it's good to keep your FPS down low.

if it is the Combat machine with blow back you will shoot about 380, mine shot about 389 at the hotel, anything else will shoot to hot for even the field use.

I agree with Howie, leave it alone, 380 is plennnty, plus I have quickly realized .25 bb's and accuracy mods lead me to more kills than anything else.

oh okay sounds good to me. and i actually dont have the blowback version. thanks for the tips