The general consensus is the YZ 400 and 465 are better motors. Less vibes and easier to tune. The 490 is notorious for either pinging if jetted correctly or fouling plugs if jetted fat. My 490 has had the head re-shaped and some port work and I can honestly say mine runs great and only goes through 1 plug in a 4 day dune trip (well that was when it was still in the bike). Still, the vibes are horrible. My advise is to do it to a second quad, not your only one. It's not a machine that I would want to ride alot. Mine will be for the dunes only, getting rode maybe 30% of the time. My 450 bike is a blast in the dunes! Maybe Paul will chime in here with his advice.
