Sorry to hear you got ripped off. Buying a used ATV is scary for just that reason.
But to offer some encouragement, I also bought a "basket case" King Quad 300. The difference is that I KNEW it was a basket case, so I planned to spend a couple of months working on it.
Keep your head up, don't get discouraged. Just keep at it one job at a time and you will end up with a neat little quad. There are things about the King Quad 300 that you just don't get with a more modern ATV. For one thing, the size - they're so much smaller than say a Sportsman 500, they're easier to ride in the woods and can go places the bigger quads can't. The other thing is the super low range, it's perfect for pulling trailers or for climbing obstacles.
You can still get most parts. The biggest problem I ran into was finding new plastics. Learning to "plastic weld" will help you there.
As for your current problem, my first thought was that you weren't at TDC, but it sounds like you made sure that you are. My next suggestion is to make sure you have the valve lash set properly. It can be a PITA to get right, I had to work at it a couple of different times before I got it right. Once you're sure that's right and you're sure you have spark, fuel system is the next likely culprit. I had a deteriorated rubber fuel line that had collapsed and was blocking fuel flow. It made me crazy, I KNEW everything else was right and it still wouldn't start. I went through everything you're going through and even sent the head off to Millenium Tech and had them do a valve job.
As long as you don't give up, you'll get it eventually.
So Iíve been a member for a couple of weeks but havenít had a reason to ask any questions till now. I got ripped off last year on this quad and donít care to explain it all. Just understand I paid too much for a machine that ran/drove but the guy was definitely not a mechanic. Iím not either though, I do know you canít wire the starter positive ground and expect your wiring/battery to last all that long. I wish the fella I bought this pos from did.
So my wrecked out 97 king quad needs a new intake valve but I went ahead and lapped what was there and got it to seal and reassembled. The new one is on order but I figured I can get it going and wait till that valve goes out of adjustment before tearing it down again.
I couldnít get it to fire once assembled. Seems like it farts a little but not enough. I pulled the valve cover to verify Timing chain and TDC alignment, ‚úÖ
My new question is, can I have the spark plug firing 180* out of order? Or maybe on the wrong stroke? If so, can I fix the wiring end or would I need to remove the cam and rotate the piston through another stroke to get me back into time between the compression stroke and ignition timing.