this is your problem,
http://www3.telus.net/cbradley/Engine_Specifications.html
now just doing slight intake and 3" after the stock manifolds then your just shooting yourself in the foot for maybe 5 hp.
carbs are easy bigger carb and headers and intake will be big hp cause you are increasing air fuel and exhaust.
on a fuelie improved air flow and exhaust flow wont count for much when it will only give you x amount of fuel at y kind of conditions.
you either need to scratch the efi and try for oldschool power, or reprogram the pcm and start upgrading the injectors.
also What do you need more power for ( I know this is a stupid question who doesn't want more power), what are you drag racing this thing up and down the street with 35's
ive seen 4cl suzukis with 38's slaughter a mud hole with the right gears.