So after replacing the crankshaft in my 03 YZ450 I got it together tonight and could not start it. I bought the bike seized up so I don't know anything about it before hand. So far I have checked spark and I do have a strong spark. I am wondering if it may be a cam timing issue. Is it possible to have the spark at the wrong time of the cam sequence, could it be 180 off in relationship to the valve events. When setting my timing I aligned the flywheel with the mark and then installed my cams. This is my first time but I am pretty sure the timing between cams is correct (12 pins between them with a dot on each level with the horizon and also a dot pointing straight up). When trying to start the bike it does not even attempt to fire up. I have tried a little starting fluid also with no luck which leads me to believe that it is bad ignition timing instead of a carburetor problem. I guess the manual doesn't explain it well but it seems to me that the flywheel passes the pickup every revolution but the spark plug fires every other revolution, so if you are assembling your engine from nothing how do you know if you are at TDC when it should fire vs. TDC when it shouldn't. Well thanks for any help you can give me, and let me know if you have any questions regarding the situation.