So I'm at the point of tuning my '71 XB1. I was getting a popping exhaust on the left (sooty, dry). I fiddled with the ignition (Pamco) and got a pretty decent idle. However it would eventually slop out and die. I checked my coil, my plug leads, my plugs. All good connections. Plugs are sooty and a little wet from gas. Checked as best I could for air leaks. (Mind you, the right cylinder is working perfectly the entire time). Checked valves and adjusted to spec. Also have some oil leaking from the left exhaust valve cover. So I go ahead and put my old VM34 on the left side and bingo bam-o, the left cylinder is running perfectly. But now, mysteriously, the right side is popping and producing black smoke. What the hell!? Also the bike doesn't idle, and often gives a big back fire through both carbs as it dies out. Is this a timing problem? Is this a carb problem? How did the issue mysteriously change sides when I interchanged the carbs? I'm dumbfounded.