Newbie here to the forum and as a Vulcan owner. I just purchased a 1997 Vulcan 750 with 22,000 miles. I recently replaced the exhaust with Vance and Hines Cruzers. I also replaced the stock air filters with K & N filters. I replaced the main jet in the carb to a 135 and a 138. Same problem with both jets. As soon as I hit 5th gear and try to cruise about 55-60 @ 4k RPM's the bike runs rough and sounds like it is missing. I checked the carb vent house that is supposed to be in the intake ear and cut it at 45 degree angle and tried relocating it- still have a problem. Is the main jet still to small? Please help. I really like this bike and I am starting to wish I never started modifiying it. Thanks.