Ktm 450 xcf

Are you getting fuel to the carb?
Is the fuel making it through the carb?
Do you have a bright blue spark at the plug?
Have you checked the OHMs reading at the coil, both primary and secondary?
Have you checked the cam timing?
What is your fuel screw setting?
Remember the basics.... To start you must have fuel, compression and spark at the correct time. If any one of these basics have issues, you will have starting problems.

Paw Paw

What year is your bike? With the lithium battery, you must hold the starter button for 5 seconds, release it, wait till you hear that humming sound, wait 30 seconds (put in your helmet, boots etc) and then go start the bike. It will fire instantly. The battery must be "woken up" and warmed up prior to just holding the start button waiting for it to start. It WILL NOT start unless you do this. I have a 2016 Husqvarna and this is what the dealer told me to do.

One way starter bearing. Will crank and crank, sound like its want to start.... it the failed bearing will not let it fire.

Very few cams go bad, but cam timing does get off due to worn cam chains.
If the valves are set too tight it will give starting issues.
Backfiring through the carb normally indicates a very lean condition.

OK, here is what I want you to try and I already know many folks will say I am crazy and that is ok....
1. turn on fuel pet cock.
2. Pull out choke on carb.
3. Turn the idle screw 1 turn clockwise
4. Now twist the throttle about 5 times.
5. Now crank it.
6. After 30 sec of run time push the chock to the off position.
7. After about 1 min run time turn the idle screw about 3/4 turn counter clockwise.

Paw Paw