I have been down this road many times with customers. If you are lucky enough to have just caused minimal damage, then you are looking at a burned valve and damaged exhaust valve seat, possibly a bent valve if the melted strap particles were passing through and the valve caught it while it was closing. These little 3 valves have EXTREMELY thin and weak pistons in them. Just because its not blowing smoke or saturating the plug with oil doesnt mean a piston isnt hurt. It could have broken a ring land. A leak down test or scoping the cylinders is really the only way to tell for sure, but the last time I saw a plug like that, it ended up causing major engine damage! take the intake pipe off and open the throttle blade and run your finger along the bottom of the intake or look in there with a flash light and if you have a puddle of oil, then you might want to go get a bottle of jack daniels man! I have a leak down tester with the special adapter for the 3 valve heads and a bore scope if you would like me to take a quick peak for you.
