Everything Random and others mentioned are true, whoever told you that "dumping" in more gas is the key to more HP is "smoking" something. From my experiences with Honda's and Nissan using stand-alone FMU's and a Apex-i S-AFC, I have come to find that high compresion 4 cylinders actually make MORE hp when tuned to the lean side of stochimetric. In fact, you want your engine leaned out almost to the point of detonation. (this is where the SAFC comes in handy, as well as a very good knock sensing ignition system). The only drawback to running lean is extra heat, hence detonation. If running a turbo setup, this is where your EGT gauge is worth its weight in gold! Dumping in more fuel, will only hurt your power as well as "clog" up your cat and O2 sensor, the only benifit to more fuel, is it "cools" down the engine. I would suggest what Random said earlier, and get some good books and READ, READ, READ! (Corky Bell's book is excellent for max EFI tuning). There are no secret HP tricks, or easy shortcuts! Good luck.
-Andrew