Hey folks I have a 2004 yz250f I'm having issues with all of a sudden. Here's the deal. I did a top end rebuild. Adjusted valves to spec. New plug. I have about 3 rides on the bike since then. Bikes always started in 1 or 2 kicks. So I had to replace the clutch and throttle cable last week. Bike sat for a week maybe 7 or 8 days total and now it won't start. It's getting spark. I took the carb apart and did a major clean. I tried to bump start it and it tried running but sounded like it was running with the exhaust plug in. Checked timing and valves again and all are good. Bike backfires every like 10 kicks too. All work was done by a professional mechanic. Can anyone help me with this?