I have a '84 KLR600. It will fire up but I cannot keep it running. I cannot choke it enough....seems like it is getting to much air somehow. I know the choke works on the carb, but I have to stuff a rag into the air box intake to keep it running. After it warms up I can take the rag out but I have to leave the choke all the way on to keep it going. It revs normally and seems to run ok. The bike is completely stock. Any ideas?