Hi, my description is lengthy, but I tried to provide as much detail as possible for troubleshooting. I'm seeking technical input re: a continuing carb issue w/my '96 Magna, which would not turn over at start up (after 5 mo. winter storage). Instead, fuel overflowed from the float bowls. We drained the float bowls, attempted to dislodge stuck floats by tapping bowls and tried restarting, which resulted w/fuel overflowing from right from carb again. Two years ago, in 2009 the carbs were pulled off, the jets and float needles were replaced, seats polished and air filter, plugs also replaced. Post carb service, I added Star Tron to the fuel. Subsequent start-ups were rough, but once running, performance was good. This spring, after failure to start, we pulled the carb bank out and had them disassembled and ultrasonically cleaned. Carbs were reassembled with new parts as needed: gaskets, o rings and choke plunger and bank was bench tested w/fuel, 1 hr - no leaks. Spark plugs were changed, the carb set was reinstalled, air box reassembled, hoses reconnected and bench test performed. Started on 4th-5th crank w/ 1/2 choke. Then the old fuel was drained from the gas tank, the petcock was removed, cleaned and reassembled and the tank reinstalled on the bike. Then, restarted w/no choke, idle rested at 1200-1500 rpm. Let sit it overnight. Next day, I added 1 gal of gas and started up w/ 1/2 choke, w/petcock in 'on' position but w/throttle, it lost compression and stalled. I repeated this step a couple of times w/same result. Finally it started and when I engaged 1st gear for a test ride, it stalled. So, I switched the petcock to 'reserve' and it started up immed. and rpms held at 1200-1500 and was steady w/giving it throttle. Took the bike for a loop around the block running on 'reserve' and it seemed to run just fine. My question is: why won't it maintain an idle and rev w/out stalling when the petcock is set to the 'on' position? This this still an issue related to the carbs? Is the petcock shot? Or is this another issue all together? Thank you for whatever input you can provide.