[Mike 4.6]

I have a 2004 recon 250 and i bought it pretty cheap in hopes of getting it running. I have done extensive motor work to all of my motocross bikes and rebuilt a few honda trail motors for my buddies but i cant get this thing to start for the life of me. the bike turns over and fires but wont start. i have done all of the following to no avail. i rebuilt the oem carb, put a new solenoid, new starter, new cdi, new coil, countless spark plugs, new top end and timing, head rebuild, and i also bought another oem carb. everything in the motor is to spec and i have adjusted both of the carbs to service manual spec. the bike is getting good hot spark and the compression is good... i`m not sure how many psi off the top of my head. timing is dead on and the valves are in adjustment. the most i get is that the bike will fire while the starter is turning the motor over but as soon as i release the button it dies. maybe somebody can give me some direction since i am just not sure what it could be at this point. thank you for any input.