Hi everyone, I had this problem for over a year. one cylinder will go out after few miles but no much time to check problem. replaced spark plugs, and air filter, removed and inspected petcock, emptied fuel tank, checked venting hose but problem kept coming back. I was ready to order CDI and Coils then I read about possible vacuum leaks which I already checked but my curiosity got the best of me and went to check again and yes I pay attention for a possible leak and I hear a hissing sound.
search for source and found a very small diameter vacuum hose disconnected from a tee between 2 carburetors. reconnected hose and after 200 miles bike is running fine
