Im new to atvs just got a 86 trx 125 for my son its a little rough around the edges but was a gift from a cousin who says theres no doubt its a solid running engine.. the problem is there is no spark from what i have read on google searches this is a common problem but i still cant pin point the cause.. i would appreciate a troubleshooting checklist from someone with more knowledge on these atvs, heres what ive done
New plug
Cleaned magneto
Checked wiring to coil and in headlamp
Checked fuse
Replaced coil with extra from a 125 pitbike

It does NOT have a battery in it with this prevent it from starting?

Any help would be greatly appreciated