I'm a big duner and like most duners will tell you, 2 strokes are the king of the dunes. More and more four strokes are competing for the title though, and four stroke is the only future of atv's to come. So try a four stroke, but build it. I too did what your talking about, I had a 250r and i got tired of always replacing the top end and little parts. I fixed it for the last time and sold it. I went to a 400ex turned it in to a well built 440 and competes with just about everything (except for those crazy built duner banshee's that the motor has to be rebuilt 2 times a year) in the dunes and i don't have to fix anything after a long trip!
2001 Duncan Racing National 440ex
Power Cylinder 4000 12:1 JE
web cam 463/9i, port & polish, 3 angle valve job, hardend rockers, titanium valve springs.
Duncan Racing Fat Boy 4 Exhaust
1mm oversized blackdiamond intake and exhaust valves
15 point gusseted frame powder coated candy apple red
Doug Eichner Signature Series Edelbrock Carb
Procom CDI ignition
Hinson Basket, Removable Side Case
Sparks 8 plate clutch
Custom graphics and seat cover
Custom air intake with K&n Filter
everything is polished and billet
Roll Design chrome swing arm
Elka dual rate ssd with LT linkage
TCS ZPS, douglas ultimate billet beadlock wheels with Maxxis Razr's
Roll +1.5" chrome anti vibe stem with Tag T-2 oversized bars cr hi bend
Herrmann arms Trail Tech HID Lights w/ custom billet mount (for the dunes)
Overized UM vented oil tank FST oil cooler kit and even more