cluefinder

Hello My name is Rob and I am here at the Moment to ask for help. I own a 2005 Sazuki Boulevard S83 VS1400 k5. I have owned it for almost two years now and have 3500 miles on it. I dropped it once almost a month after buying it. that was a 1500 dollar lesson that I will not soon forget. after getting it back from the mechanic having put new exhaust and jetting it for me it ran fine. took it in cause it was backfiring at idle and when decellerating. he said he could not find a problem took it apart multiple times the problem fixed itself said there was probably something caught in carbeurators and it fell out when he took them apart. the bike ran great other then occassional backfire more like soft pop was told it was just fuel that didn't burn hitting exhaust nothing to worry about. Now It starts up just fine will run in neutral just fine. It will run great for about two miles then it will stall for no apperant reason Like someone hit the engine kill switch on me. after the bike rolls to a stop and is in neutral the bike will start like normal and will idle fine but as soon as you press the shifter down into first it will stall everytime with clutch engaged. and almost without fail a loud backfire will follow about 1 second after engine quits. I was wondering if there was anyone who could shed light on my problem for me? Sorry for such a long post.