hi i have had my bike a little while, had no problems til the thread got knackered on the head then it decided to crack, replaced it with a standard 125 head and piston, now when i try to start it, it will try and try then backfire and try some more but wont start. it was working fine before even though the head was wrong and it had piston slap, the spark is sparking petrol flowing and 2 stroke lubricating, i cant see why it wont start as all i have done is replace the broken head and pistons,
please please help if you can as i love this bike and dont wont to blow it up which was on my mind after trying for 8 hours to get it working