the atv has a fuel injection and the 2 cycles and 4 cycles we use dont,its the old school style carb. fuel injection requires a 'brain' or computer to meter how much fuel is being delivered to the engine by different sensors such as o2,throttle,and temperature sensors. where as our carbs are gravity fed and metered (depending on the carb for our engines) thru mixture and idle screws on the carb itself and has no computer, so no 'chipping' here on these engines.
IMHO fuel injection on our bikes would be nice for better acceleration and throttle response, however it would be a nightmare of electrics and the more stuff you put on an engine like this more things go wrong,also the cons way out way the pros on stuff that i just don't need. if you want to push more horsepower out of one of these engines try looking at some of the topics here
High Performance Bicycle Engine Tips - Bicycle Motor at Motorized Bicycle Forum what it really comes down to is modifying restricted ports and buying better parts for these engines.just like the old days of before fuel injection. like taking dads old chevy 350 boring it over,putting a better cam in it,roller rockers,holly carb and so on...