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Kids couldn't start the 50 yesterday -wouldn't fire at all. Checked ignition key, kill switch -all good. Pulled plug, looked ok, but no spark? We are new to maintenance past oil changes/air filter/chain/suspension/etc. Any ideas on what to check next?

The last time you cleaned the air filter did you take the complete housing off? If so Check the ground wire for the coil that connects to top housing bolt. you may have forgot it. Just my 2 cents.

We have never completely taken the housing off, plus, it has run since last filter cleaning...

if you checked all your killswitches/keyswitches i'd completely disconnect them to where its not grounding out anywhere, and if you dont have spark look into your stator and trigger coil (not fumiluar if dirtbikes have triggers on em') and check the resistance.. if there good i'd look at your spark plug coil.. on engines you wont change alot of coil's, unless the motor has another problem.. they hardly go bad, all they are is a winding of wire. also look closely at the wires going to and from the coils. you'll probly get spark if you disconnect you're ignition switch.
hope this helps, if im wrong about anything someone correct me, thanks. -joel

try a new spark plug

left that one out it might just be that simple.

...turns out it was the spark plug I guess my lesson was getting to know the entire electrical system intimately.

i just got done meeting mine. after rebuilding my whole engine putting rings in it and a new head and valves. it stopped sparking and i replaced all the coils on the stator plate, replaced the CDI and tested the main firing coil and that was good. only thing left was the wiring. well i found a broke wire under the insolation an it was as simple as that.