Hello, I have a 1980 XS650 that is stock except for UNI pod filters. I am having trouble with the jetting on the bike it has stock carburetors as well. The previous owner changed the main jet to a 140 when he did the filters. At first, it ran well then it developed a surge taking off from a stop and seamed a little rough between 2000 and 3000 rpm then it clears up. I have tried other jet combinations with no luck. I am running 91 octane Non-ethenol gas in it as well. I have done fresh plugs a few times as well. If anyone has a suggestion on what might get rid of the surge that would be great. Thanks