So... after rebuilding my KX65 pitbike I had the confidence I could rebuild a 4 stroke, and as I turns out I can’t at least not yet. I bought a 2005 CRF250R off Craigslist for $550 and put a new crank, bearings, spark plug and gaskets in the bike (copper shavings were in the oil). But it just won’t start after getting it back together. It has back fired a few times and sounded like it wants to start but won’t. What can I check besides the timing and valves? Am I just not kicking it hard enough lol maybe I should stick to little 2 strokes. Thank you very much for any and all help!