1998 Honda Shadow 750 ace. Has been sitting for about 3 to 4 mths. I tried to start it yesterday and it would fire up but would only run for two to 5 seconds then go dead. this was on full choke. After 15 minutes of this back and forth battery went dead. Got the charger out. After another 30 minutes i finally got it to run, but only on full choke. I finally got it to run off the choke but only if giving it gas. When you let go of the gas, it would bo dead. Also, when it was running on full choke, only the back cylinder was firing, exhaust was coming out of the pipe for the front cylinder, but it was cold. It never heated up untill it I was finally able to throttle it. The front cylinder backfired a lot. I changed the plugs tonight but it has not helped. Before this time it had been sitting for a few months and was hard to start but finally picked up and ran. What could it be? Carberator, jets?