Ktm 450sxf 07 wont start

Drain oil. Use degreaser to clean area. Use JB Weld & allow to set up properly before adding oil.

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hello
Back fire is an indication that the bike is firing incorrectly.
Your timing chain is probably stretched, due to the year.
inproper valve timing due to stretched timing chain will make the bike backfire.

I have other thoughts like stuck valves or inproper sparkplug wires on wrong plug,
i always start with easier and less expensive method.
1st check your sparkplug wires to make sure they are on the right plug.
2nd pull sparkplugs and do compression and leakdown test.
3rd pull componets to see if valves are opening and closing, (valve clearance check)
4th if valves are good, then timing chain is probably stretched.
5th if timing chain and timing marks are good, and valves are good, then proceed to
testing the signal generator to make sure your getting a signal to the cdi,
6th if you have a signal to cdi, the cdi tells which coil to fire. either # 1&4 or # 2&3.
if signal generator is working, but coils aren't firing right then its the cdi.
obviously your coils work because its firing, just back firing.

Thats all it could be from easiest to hardest.
Good luck and have a great weekend.
Big Al

If you are able to use a digital volt meter and work your backwards from spark plug wire to coil to cdi to stator you can figure out where voltage stops.thats a fairly newer bike unless you really submerged that bike under water i dont think its the cdi box.it could be coil wire it could be coil.you want to check or change the cheaper parts before you go right to cdi because there not cheap.I have a yamaha banshee 350 and she was breaking up real bad.I thought because it was only happining on top end that the cdi was breaking down or stator was going bad.Found out with meter it was the coil wires and spark plug boots.These items have to have a certain amount of resistance or the do not conduct correctly.And spark plug wires and boots are not that exspensive.So thats why I say start from sparkplug boot and work your way back.Try that and Good Luck.

Does it still have the original sparkplug cap? If so, from it's age, the resistance
in the cap has increased past it's optimum performance. Replace the cap or
(if possible) pull the resistor out and run it direct from the coil only if it's a
points style ignition not a CDI.
The resistor cap was put on all engines back in those days so it wouldn't interfer
with radio and television transmission signals.
Now days with CDI (capassitor discharge ignition) they need resistance on
the wire or cap or both, to clean up the high voltage going to the spark
plug so it don't hurt the CDI. Running a old engine with points with no
resistance wont hurt a thing.

I'd start with simple things like checking the plug and doing a few electrical tests.Some tests you may be able to do yourself like resistance checks.Compare the following spec with what you get ; Primary coil . 25~35 0hms Secondary 5050~7550 Valve clearance inlet 0.10~0.15 exuast 0.15~0.20 both cold and in mm.

ok buddy on carb will be a screw try fiddle with this mixture screw on carb below get back to me with results

check spark,timing from side case side,then swap spark plug,try to bypass spark cap,then check flow of petrol to carb,clean carb and allow to cool if needed.Sometimes a coil just dies for no apparent reason..The last resort is to swap the coil inside the side case...

Will it turn over at all?

Hello.

Sparkplugs. That will fix it.

You can choose between 3 types the normal the cold and the hot (performance) sparkplugs. The normal for medium temperatures is the best, the cold is suited for bellow 5º C temps. And the hot is for hot weather and performance usage.

Hope that helps.

take your carb out, clean the entire thing, that means every nook in that *****. do this and if still a problem write back because in most cases were n idiot is involved, this is the most over looked problem