I'm no mechanic, but I've had success with rebuilding things in the past so I figured this wouldn't be too bad. I was wrong. I recently purchased a running 2006 yz450f from a co-worker and he suggested that I replace the cylinder and piston before doing any heavy riding. He came to this conclusion from recently having it apart and installing a new timing chain among other things. When I got it, it would start right up and had zero issues with plenty of power. I've since replaced the piston and cylinder and now it won't run. I've not tampered with anything else and put everything back EXACTLY as it was before so I'm stumped. Timing is absolutely perfect without a doubt. A couple of times it would start for a split second then die. Occasionally there is a pop when kicksarting (assuming a backfire), and it constantly leaks gas when I'm rapidly trying to kicksart it. Can't get it to fire anymore at all. Don't know what to do so any advice would be helpful. Thanks!