Lighter BBs are more dramatically affected by hopup. 0.25g min...0.28/0.30's are better.
Pull back the dust cover and you'll see the little dial there. Clockwise puts more on, counter clockwise takes some off.
Sounds like you need to take some off. You want your shot to go straight out...then just drop at the end.
If you find that you're having a hard time setting it...some things to consider:
- quality BBs...BBBastard and Madbull ones are very consistent (size, weight and finish)
- different hopup rubber (if you're using the stock JG one it's pretty crappy)
---a good hopup rubber will grip each BB consistently and will have enough cushion/play so that you can put fine adjustments on how much is applied