Originally posted by: CTATV
I dont know if it can bend a valve but I know its definatly not great for your motor to rev the crap out of it when it isnt in gear. The motor is designed to rev that high when under the stress of moving the quad. you can definatly overrev your bike when there isnt any force its pushing against.

Originally posted by: 95wolv
First let's get back to the symptoms you described : revved up, black smoke, let off gas, backfired,now runs badly, ticking noise. I fully agree with everyone else, sounds like carbon fouling, the plug shows that, now for the rest, it may be possible a small hard carbon chunk got caught under the exhaust valve, not letting it close all the way, so now you have clearance in your rocker arm, so now it ticks while idling. First, I would pull and clean out the carb, getting all the passages cleaned out, then take the fuel line from the tank, and drain out all that nasty old fuel into a bucket. Fill the tank with fresh clean gas, and put about a half can of Sea Foam in with it. Start it up and let it run, blip the throttle occasionally, hopefully the Sea Foam will loosen up the carbon in the cylinder, and maybe clear out the valves, you may need to go for a ride to really warm it up. If it still ticks bad, like azdunerat said, you'll have to pull the tank and check your valves, the lock nut may have worked loose, and it will only get worse if you don't check it out !!!

Originally posted by: AZDUNERAT
The ticking sounds like your valve screw has come off, common on these motors. You need to dissaseble the bike some(take off the fuel tank) and open the valve cover and there should be a screw on each one of the valve adjesters. That is what happened to my wifes cousins bike, only his screw worked its way into the case(crappy). I would try that. As for the screw when was the last time you cleaned your air filter. You could be chocking the air flow causing the rich conditionAaron