I just purchased a used 06WR 450 with the boyeson carb kid, DRD pipe, no toil type air filter, and a bunch of cool accessories. The bike runs really nice, and feels very well sorted with one annoying exception: at sustained speeds on pavement it has a little miss you can hear and feel, occurring every 20 seconds or so sometimes. Other time every 10 seconds, sometimes once a minute. It seems not to be engine load related, but I don't feel it on full load acceleration. It just occurs on simple comfortable rpm sustained speeds and may or may not be present at any given time. I did change a spark plug to no avail. I have had to loosend and retighten the header to get the dang oil filter screw out and thought perhaps I had some koind of exhaust leak effect, but it runs so good I do not think that is the case. Any ideas?