I have an 06 450X that I purchased new out of the crate about six months ago and now I noticed it is backfiring louder, has overheating problems and it has lost the 'edge' on its power. This is what has happened in sequence since I bought it: 1. As soon as I got the bike home after buying it I removed the radiator louvres (fins) and installed a radiator guard. I also installed a plastic Hyde racing skid plate. 2. The first breakin ride was at Ocotillo Wells, I rode the bike for an hour at slow speed 25MPH) with no problems until I was T boned by a rhino. Dislocated knee, bike was fine with the exception of a small dent on top of the radiator, the small fins were unaffected. 3. 3 months later my knee is repaired and I ride again in Dove Springs. We got to 6000 feet and run into a little snow which slows us down, my radiator immediately starts boiling and I smell coolant. I let it cool and go home. 4. I then added a wetting agent to the coolant to help with the cooling. Once again I experience the same overheating problems on other rides in soft sand trails or when riding slow with my 8 year old boy on hard pack. My buddy also mentions he can hear my bike backfiring, which I thought was normal. I also had to refill the overflow tank with Honda Coolant after two other rides, per the instructions in the Honda Owners Manual. The radiators themselves have always maintained fluids. 4. After reading that the 450X runs lean to meet CA emmissions, I took it to my bike shop to have it rejetted from a 45 to a 50. I chose not to modify the airbox or exhaust as it ran fine as stock with the exception of the overheating. After getting the bike back I noticed that the bike is now backfiring significantly louder and the power of the bike when I get a little speed up is sluggish nearly bogging. No more power all the way through the power ban and no more fun! I get on a single track with my son for a few minutes and the bike also boils again...aaagh! 5. I send the bike back to the shop and they called me today and said the radiator has good flow, the cap pressure is fine but the pressure in the radiators is building up too quickly. They suspect a leaking head gasket or cracked cylinder....what?!!! It's a new bike, I'm 38 years old, I ride like a grandma and over maintain it! How could this be? Any thoughts would greatly be appreciated?