Tharamorn

I have a 1979 Dt 125 mx and am having problems getting a constant spark. I've replaced the coil, plug cap and plug also I have rplaced a lot of the wire connections with new ones. After doing this I kicked the bike over and had a very strong and constant spark, put plug back in and tried but got nothing so i removed plug cap and checked for a spark with a new plug and there was nothing. 5 mins later tried again and got a spark all be it a weak one, then nothing. Can anybody give me some advice please.