Andy is right. Shift on the fly is OK for the new 04-05 push button type. This puts the front in limited-slip mode where 3 wheels are pulling. It's great for making tight turns (the front end doesn't push as much) or those times where you just can't stop to engage full lock.

 

Like I said I shift in and out of 4 wheel drive as long as I am going less than 10 mph, have let off the gas and the rear tires aren't spinning. But, page 79 of the 2004 650 twin operator's manual says CAUTION Do not attempt to either engage or disengage the front differential while the atv is moving.

 

Owners manual on a Rincon 650 says don't tow over 850 lbs too.

 

and don't put over 100 lbs on the front rack or 200 on the rear.

 

Own a 05 500 manual transmission cat I got in October 04. Just went over 975 miles on it today. The only problem I have had with the bike is the 2/4 wheel drive electric actuator went out after the first month. Went into 4wd, but wouldn't come out. Took it in, got it fixed under warranty, but the mechanic said never shift on the fly. Puts too much stress on the actuator that drives a pin into the front dif. Hope this helps