More air = less power

The only thing I can think of is if the injectors on the sdi only injects fuel through out certain intervals, that the extra air is just blowing the fuel right out the combustion chamber.

reeds and or airbox mods won't be themselves make more noticable power will get better throttle responce from reeds, but on a doo I have never had any luck messing with the airbox, the theory is the colder teh air you can into the motor colder air is denser and makes more power again not a real noticable gain. NOw if you get the motor ported and pipes with reeds then you allow your engine to breath better and will see more gains.

Air boxes are good stock........reeds.......there is a little to be had, not much, but a little..........