I JUST BOUGHT A 2006 POLARIS SPORTSMAN 700 EFI AND AT FULL THROTTLE @ ABOUT 35-40 MPH IT CUTS OUT BUT IF YOU BACK OFF THE THROTTLE TO 3/4 IT RUNS FINE. JUST WONDERING IF ANYONE HAS ANY IDEAS? THANKS

 

It usually helps to not type in caps lock, it tends to annoy some people, It makes it seem like you are yelling and none of us have the self esteem to handle that.

Being that your ATV is EFI it is harder to guess what it could be, might be water in the gas, old gas, might need a new plug, or something that the dealer must "plug in" to find.....

 

You've probably got a bad ground. Check where your grounds are connected to the frame. This happened on my 500 x2. It would cut out and pop and carry on. Found the ground screw loose. That cuts out the computer, etc and causes it to cut out.

 

could be loose ignition connections, water in the fuel, low battery voltage, Clogged air filter, electronic throttle malfunction, or could just be lean or rich fuel! just a couple things to check. depending on age of atvm the injectors might need replaced or cleaned, that could cause high rpm/speed loss. also the electonic control unit (ecu) might need work (worst case scenario) and the dealer would have to help with that one!

 

is it cutting out or back firing. water, bad ground tends to make them want to back fire.

 

The first thing I would suspect from your discription is the TPS sensor.
(Throttle Position Sensor)