grizzly 700 wont start
 

I took my head off to get resurfaced and to replace the head gasket. when I put it back on I properly aligned the cam and flywheel marks and tried starting it. when trying to start it just backfires. when holding the throttle open it fires out the intake. I flipped the cam 180 degrees and had the same issues. put a straw in the spark plug hole to make sure that the tdc mark on the flywheel was correct and it was. I don't know what else to do. any answers?

Flipping the cam 180 is exactly the same as turning the crank through 360 so doesn't make any difference on "dead spark" engines. However setting the valve clearances 180 out on the cam will make a difference, did you?

I set the valve clearances when the mark on the camshaft gear was pointing up as though the engine were at tdc

Sounds like you did set the valves on the correct TDC, to double check, turn the engine by hand in it's normal rotation direction, watch the inlet valve close and then watch for the TDC mark to come up on the flywheel, then check clearance on both inlet and exhaust valves.

checked the valves as you suggested and they were to spec.

Have you done a compression test since the rebuild, and did you grind the valves in when you had the head off?

yes I did. around 70 psi I think. checked out in the service manual. didn't grind the valves but they held gas with the head upside down.

70psi seems low. It is difficult, with automatic decompressors, to know what is right. I have just fitted a new piston and rebored cylinder to an Eiger, checked compression afterwards as it didn't run, and comp was 100psi. (Reason for not running, plugged exhaust!)

it says right in the service manual with the throttle open 70 psi is on the high side of things. page 3-26

You seem to have covered mechanical issues. How about fuel or ignition problems?