I recently picked up a 96 xr400. Factory everything, no mods, 162 main, i think it has a 65 pilot, have to re check on that one. It has been sitting for a few years. I completley cleaned everything out, went through carb, put new internal tank filter and external filter. Got the bike running. Starts and idles perfectly, when i rev it or ride it. It stalls after 1/4 throttle, if i rev it and try to feather the throttle to keep it running it spits out black smoke. I put new plug in and it is covered in carbon. It's almost like it's being shut off or after 1/4 throttle. Or loosing spark or a ton of fuel is being sucked in for some reason. If i put the choke on it does not change, i have adjusted fuel screw with no change. It will not run after 1/4 throttle no matter what you do. Has anybody experienced anything like this?