Overspin with G&P M120 motor
 

I have a G&P M120 high speed motor pulling a Guarder sp110 spring, which I hear is supposed to be equivalent to a m120 spring, my batt is 9.6v and i have some serious overspin issues. I'm not too sure how to go about correcting it at this point, any advice is appreciated.

Have you chrono'd the gun?
Guarder is notorious for improperly packaging springs

its shooting in the ~200 range, i think it is the right spring though, i tried firing with a 8.4v battery and it had a little trouble but still did more than one cycle. There are more problems than just the overspin (air seal and possibly barrel suck) as it may be pulling the piston back before the first bb leaves the barrel (590mm on my rpk)

200fps is extremely low, it should be around 400fps, and a 400fps spring certainly shouldn't cause cycle overlap on a 8.4v large battery
What is the ratio/brand of your gears and motor?
If you have higher ratio prometheus gears, a light spring and a weak magnet motor (IE TM, CA, ICS, G&P M120) the momentum carried over from the heavy gears will cause overlap of 8-10 rounds on a 9.6v large battery, less on an 8.4v large.

I know it should be around 400, that's what i was shooting for; so to speak. I've got stock JG gears with a G&P M120 motor, which is why I'm having trouble figuring out my overspin issue because it really shouldn't be this bad. The battery cells are sub c.

Go back to the stock motor? or you coulda stripped something.

the stock motor can't pull that hard of a spring, and nothing is stripped, all my gears and piston teeth are fine.

airseal. Has nothing to do with overspin of the motor.

As i mentioned earlier, I'm aware of an airseal problem (which is easy to fix), but overspin is the main issue i need to fix as it can cause other nasty problems with feeding and jamming my barrel.

overspin won't cause feeding or jamming issues.
It's no different than shooting semi auto and letting off the trigger half way through a cycle.
If your having jamming and feeding issues, that's something completely different.
Jamming would most likely be caused by your airseal problem, and feeding issues could be anything from airseal to improper shimming, to mags, to setting your hop up too high.

Ya i think its mainly an air seal problem and maybe barrel suck because of the high ROF and long barrel since nearly everything else has been eliminated. Thanks for the replies.