[Johnson31]

I just bought a 2016 sportsman’s 450 with 38 miles on it. It did fine for first few days but then started to die at idle. After a couple more days it back fired and died and would not start again unless holding down throttle but once letting off throttle it will go to idle rough and die.

what I have done so far is

confirmed fuel pump works

emptied tank of old fuel and replaced

replaced spark plug and made sure it’s sparking

pulled injector out and watched it spray fuel while trying to start

butterfly on throttlebody opens when throttle is pushed

any help on where to go from here?

 

[Mech]

After it dies pull the spark plug straight away and see if it's flooding or running out of fuel.

Check the air cleaner.

You could also check the temp sensor that tells the computer what temp the engine is. It might have two temp sensors, one for the fan and one for engine management. If the efi temp sensor is crook it might run too rich or too lean.

 

[Mech]

You could also check for trouble codes..

You could look for hoses off or air leaks into the inlet manifold.

You could check the valve clearances(less likely if the problem arose suddenly).

Make sure the spark plug is gapped right.