nanabecky

i just bought my husband a 1979 yamaha 1100xs. it now seems to have an oil leak but we can't tell where the oil is coming from, it only seems to leak when he is riding it, the first real ride he was able to take it on is when the leak appeared. he even found oil dripping out of the air filter compartment, so we replaced the air filter. and he had found a loose hose clamp which he thought was the problem. so he replaced that but today when he took it out again the same thing happened. He did say he left the gas tank on choke when he rode it, i don't know if that could cause a problem? if anyone has any suggestions please let me know.