1985 spark help

[davidonmars]

Hey do i bought a 1985 cr125 last night... Compression is 150. I put a new plug in last night and it started right up... cleaned off the flywheel because there was a bit of rust on it... So last night it ran and this morning it ran no problems... I'm about to load it on the truck to go for a ride and i start it up it starts then it dies... Its electrical because i can hear it die on me... then it might get a bit of spark and come to life then cut out again... So i pull the plug and check for spark... sometimes there is spark, and when there is it is blue and theres a nice colour... and other times theres no spark at all... Any ideas... Its got a new plug in it as well