The only thing more reliable than these 350s is maybe the old 300 Hondas
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yep you can beat the reliability of the ol' 350s. if you don't mind changing the oil every other ride and checking/shimming valves then go for a 450. If i was to get a 450 it would be a Honda. one less cam easier to check the valves and time the motor.
As much as I like Honda, the 450r is the only one that uses shims(far as I remember), so it wouldn't be on my list. DOHC is easy to time, especially on these small engines.
I actually had a 1989 honda fourtrax haha and I agree they are super reliable.
Biggest con is no reverse, really. It is going out handle a 350, out power a 350, feel better then a 350, etc... However, the 350 is still a damn good dependable bike, that likes to be modded. Also, very cheap to repair, and is great in the woods. Not that a 450 isn't.
Actually, the warrior is 70's tech. I need reverse becuase I have trails that are too tight, and I explore a lot. Need reverse when you are in boulders and stumps.