Motorcycle Repair: No mid range power, airflow rate, petcock

Question
I recently had to change a petcock on my 1981 suzuki gs750L. the bladder had blown and was causing gas to leak from the #2 cylinder.
After replacing the petcock, the bike is a total dog past 2000 rpm, then it takes off again after 4500, but for several seconds it really has a lot of problems, sputtering and dying out.
I have also replaced the air box for 4 clamp on air filters. this was much easier than trying to fit the carbs and air box back after realizing the petcock was the original problem.

Any suggestions?

Answer
Hi Brandon.
 The big problem is that you replaced the airbox with something that the bike is not tuned for.  The carbs were tuned for the factory airbox, not for the aftermarket, clamp-on filters, which do not restrict the airflow at the same rate as the factory setup.  This adversely affects the mixture and, consequently, performance.

 You have two options with this.  Either return the bike to factory setup or get the carbs retuned for the new airflow rate that the new filters give you.  Chances are the bike is running either very rich or very lean right now.

Good luck.
FALCON