2001 ktm 125sx spark plug issue

So I recently rebuilt my 2001 ktm 125sx and it was running mint for about 2 hours then suddenly it stopped working/wouldn't start so I took out the carb multiple times at the track and cleaned but that didn't work so when I got home I took out the spark plug and it was giving very very faint spark,it starts first kick when cold but then dies nearly instantly then doesn't start again for ages,what could be the problem? I was thinking coil or cdi box but not to sure.