My 1982 Honda Nighthawk 450 is sputtering at takeoff. Whats Wrong?

okay well i bought a 1982 honda nighthawk and it only has 8300 miles and ive rode it now for about 2& 1/2 weeks ran GREAT but i took the pipes off where it splits half way down and started it and it ran for maybe 6-7 minutes and put them back on; now all the sudden it is sputtering at take off and its only if i give a little gas. if i hammer it it runs fine but its just at the beginning of the throttle. ive put new gas in it, bought new plugs, and im stumped... normally im good with this stuff but i just cant think of anything more unless there is something clogging one of the carbs a little but other than that i dont know. any advise would be great, i will be happy to try anything at this point.