Yes you can run topless without some sort of fuel management but it will exacerbate the stock lean surging, etc. and you won't see any real increase in horsepower. I've got the D&D slipons and I drilled the airbox cover. I had a Race Tuner done along with dyno tuning. The difference was amazing. the bike now runs great, no lean surging and the fuel economy only dropped a little. Pricey (about $1,500.00 at the local Harley dealer for everything) but it was worth it for me.