I have a 2001 Katana which ran great until my stock carburetors eventually got so clogged that cleaning the jets and ports wasn't enough to even get it to start. I bought a set of used carbs off of an 04 Katana which solved the problem, but my engine has started excessively backfiring ever since. It will do it at all RPM ranges, idle to 11k, and in any situation, idling, revving, cruising at normal speed, gunning it at full power, etc. I would like to get some ideas on some possible causes of all this backfiring, so I can have some ideas of what I'm looking for when I give it a good look over.