Hey guys, i was trying to start my 250EX today, and it wouldn't go, took the plug out and hosed it down with some WD-40. Put it back in, and almost started. It hasnt been started for a wile (since the summer) and it made a reallllllllllyyyyy loud POP like it back fired but now black/brown smoke comes out instead of blue. it still wont start, but i want to make sure i didnt just mess it up realllllyyyy bad. i sure hope i didnt just bust it.  

any one?  

Take a piece of emery cloth or 100 grit sandpaper and clean the plug between the electrode and the ground "hook", or just replace the plug. Make sure that the gas is good, and for good measure, spin it over a few times without the plug in to clear the
cylinder. Put the plug back in, turn your choke on and fire away. I think your clyinder was overloaded from trying to crank it over a few too many times. Any time you need to clean a plug, use the emery cloth or sand paper and not the WD40. It is a water displacement and does nothing for the contact points of your plug.If the motor still doesn't fire, shoot a little starter fluid into the air box, and try again.If it runs just long enough to use up the starter fluid, then dies out, crack open the bowl drain screw on the bottom of the carburator, drain it out, and try again. That should get you going again.  

By the way, that brown/black cloud youre referring to was probably the packing from your muffler from an overload of fuel. Get the motor running first, and then check your packing. You may need to replace it.