ASK THE MXPERTS: MOTOCROSS DIAGNOSIS BY PROCESS OF ELIMINATION
My 2018 KTM 250SXF was running fine on Wednesday, but when I went riding on Saturday, it would start and run fine, but it wouldn’t rev. It also sounded weird. What’s wrong with it?
It isn’t easy to diagnose your problem with the information that you gave us, but, if we had to take a shot in the dark, we would guess that you have a fuel-delivery problem. The first thing we would check is the in-line fuel filter (hidden inside your fuel line’s quick release). It can be back flushed. While you have the fuel line apart, check to make sure that the O-ring on the quick release is not torn or nicked.
The second thing we would do is borrow the gas tank off a friend’s KTM. If you put a different gas tank on your bike and it runs and revs, then your problem is with the fuel pump inside your tank.
Third, prior to the 2019 model, KTM had an issue with the gas tank’s internal fuel lines kinking, which pinched off the fuel delivery to the fuel pump. The kinked fuel lines would deliver enough fuel for the bike to run, but not enough for it to rev.
In 2019, KTM realigned the fuel lines inside the gas tank so that the internal fuel line came straight from the right side of the tank to the left side where the fuel pump was located. This eliminated kinked fuel lines; however, your bike is a 2018.
Other than that, there could be ten other maladies, but you have to eliminate the obvious things first and work your way down the list.