I just recentley got an 07 yz450f for 3200, here is some background on it; It was professionaly maintianined by a head mechanic at a yamaha dealer, it only has about 30 hours on it. I have heard people talk about sucking sand into the breahter hose and I'm worried considering I was riding in sandy areas this weekend. The problem began when I was riding yesterday, The bike was running regularly, I shut it off and let it cool for a little, then went to start it again and nothing happened. It backfires and smoke comes out of the exhaust when I kick it 10+ times. Does anyone have any suggestions as to where to start with diagnostics? PS when I went to bumb start it every component in the engine was running smoothly, sounded like no spark or potentially a fouled plug? dont know much about that aspect of 450s. Any help is greatly appreciated.