My guess is that a lack of fuel is not the problem as the bike only boggs down at lift off.
My thinking is that you are running too rich dumping too much fuel to air going from idle. If the bike idles fine at around 1000 RPM and runs fine while it is under way the problem is in the transition.

Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats. H. L. Mencken