2003 VTX 1800 C. Bike has about 450 miles on it so far. It had two miles on it when I got her new about 3 weeks ago. Changed to HK sideburners at about 30 miles. Went for ride today and it seemed to develope a vibration at about 70mph. Then as the day went on it seemed to jump and pop at slower speeds with throttle part open (just crusin). Came back and pulled plugs. All looked great except to rear on the right side. A little fouled. I was reading the post about plugs fouling during break in. I also started the bike at the shop here quite a few times for friends to hear it but did not ride it alot until the last few weeks. Can I just change the one plug or do you suggest changing all 4. If it is going to foul plugs until its broke in I would rather change them as needed. Any info will be great.