sounds pretty much normal .. Buy a modified bike and guess at what's wrong with it.. Personally i'd try going with a smaller carb to improve low end power and throttle response while sacrificing a minor amount of top end.
As far as i know a carb's bowl should always be level. The float seeks a certain level. Tilt the bowl and the level can be way off. The level of fuel in the bowl determines how fuel is metered into the carb's diffferent systems. But sometimes an aftermarket carb just won't fit that way.
Anyway a tilted carb could cause all sorts of weirdness if it's tilt causes an inacurate float level.
the bike's been extensively modified.. there may be hidden problems as a result of failed attempts at more power.. the problems you describe and the solutions may go beyond normal tuning and into the realm of the engine components themselves.
Without a good running bike to set a baseline, and then modifying and testing one thing at a time, you can end up with a bike like yours. It may have satified the previous owner but your idea of "performance" (good acceleration, good MPG) and his (max power output / max top speed) are different.