I'm having trouble with my bike.  I recently was riding and hit some gravel.  I didn't wipe out but in the process I killed the engine and since I was in 3rd the rear wheel locked and I skidded about 5ft.(upright) Anyway, after that the bike chugged real hard when I restarted and smoked (grey) when I gave it gas.  I got it home but it would not idle at stops, even with the choke out.  I had to give it about half throttle to keep it running.  When I got home I parked it.  The next day a lot of oil was pooled on the cooling fins.  I have not changed the oil plug in the head cover yet.  Now when I start it it smokes (grey) and runs rough.  Also, at about 3/4 throttle it backfires a flame.  Especially if you back off of it and get back on it quick.  Last thing it has 18k on it.  thanks for any help or ideas.

but you didn't drop it? sometimes when a bike is dropped they act that way, till the oil gets back to where it needs to be.

Using the engine (turned off) as a brake is not always a good thing.   But,  it sounds like it was a panic situation and you walked away...... glad for that.  

If it does not recover and suggested by Rigidchop,  do some of the standard diagnostics first before tearing it apart.   Check spark plug looking for oil and  do a compression check.  

Also, there are basically two gray smokes, light blue'ish gray which is a sign of burning oil (hangs in the air also), and then a dark gray which can be a sign of combustion problems ( ign , fuel or compression).  So......  is it light gray or dark gray smoke?

These guys are right...

Sounds like the timing is off as Verslagy said, but why would there be an oil leak?  Need to locate the leak.

As T Mack said, oil does make a light gray smoke, but why the oil leak on the outside?

It could be a coincidental thing (but can't be sure without some diagnostic).  It sounds like, your timing is off because your tensioner gave out and you bent a valve.

I wouldn't start the engine any more just in case you have some loose parts in there...

BTW - Why did the rear wheel lock up in the gravel?  Was it because you hit the brake, something got in the belt, or did the engine lock up?

From what you've said, you do have a problem.

Thanks for all the replies.  The oil leak is that head plug. I'll definately get to that.  I keep reading about this cam chain mod. I've read the stuff in the marketplace and tech forum.   I think I might need one.  I'll be sure to  post any questions I have as I go so I can access the collective wisdom of this sage group.

I finally got time to tear into the bike with manual in hand.  I hope to attach some pics of what I see inside.  I don't know how to go about checking the cam tensioner, how to measure it. etc.  look it over and let me know what I need to do.  thanks for any help, ok pics won't post. how do I post.

I'd have a look in the air filter, just to see if crap flew up on it & now its not getting enough air. Waht crap? I dunno, but the engine needs air to run, so I'd make sure it's getting all it needs befor I went to wrenching deep.

hopefully this works, still didn't work just follow the links

http://www.bikepics.com/pictures/1163620/

http://www.bikepics.com/pictures/1163609/