Ktm 250 sxf 2008 backfires

could be as simple as water in the fuel.
kick starter issue: need to remove side cover and inspect!

could be a faulty spark plug or the wrong one.

.010" inlet hot .012" exhaust hot if water cooled
if air cooled add .002" to the measurements

When you "give it gas" you are opening the throttle.
At that point the fuel system is supposed to supply the engine with more fuel to maintain the air/fuel mixture.
Check for anything that might be clogged like filters, hoses, fuel passages, etc.
If it is still under warranty you could void your warranty
if you work on it though in this case a warranty is meaningless if you have taken it in 6 times.
I've seen models where you could replace everything and
a week later it would refuse to run.
Sometimes it's better to leave the thing at the junk yard and buy a new one but that doesn't happen often.

i would remove the clutch assy and check all parts including rear bearings ! something is failing !

Thank you for contacting FixYa with your inquiry. I have been going
over some of the older help requests that have been archieved and
trying to provide solutions for those that didn't get answered. Hope
this information helps.

Try These:

KTM Owners Manual

http://www.ktmusa.com/download.php?dataID=8101G9_OM_EN.pdf

KTM Service Manual

http://www.ktmcyclehutt.com/ktm-parts/ktm-parts-search.php?ktm-motorcycle-parts=Repair-Manuals&year=2007&ktm-model=sxf-450&fitment=bigbikes-all

KTM Repair Manuals Order Site

http://www.repairmanual.com/KTM.html

http://www.tryvod.com/search/ktm-2008-450-xcf-owners-manual-download.html

http://www.pdf-manual.com/user-guide-instruction-owner-manual-ktm-450-exc-2008-17793.html

http://www.pdf-manual.com/telechargement2.php?id=17793

http://www.mydrive.ch/browse#/

Manuals General:

http://www.dansmc.com/shopmanual2.htm

Other Manuals Sites:
http://www.fixya.com/motorcycles/ktm

Motion Pro offers a tool that is half the price of the one KTM offers, that will do the job. I got mine at Bikebandit.com after searching all over for months trying to find a cheap alternative to removing the spark plug from my 2007 KTM 250 SXF.

hi mate its a thing with the fourstroke bikes they are very hard to start when hot they take a load to get going again just keep trying and it should think about it every 4 strokes there will be a spark so .......