So after installing my gsr head... i set the timing like i always do and when i started the motor its sputtering and wont rev past 3k its chokes and wants to die.. I place my hand by the throttle body and after around 3k rpm i can feel the air being push back out the throttle body instead of going into the cylinder.. I did compression test which is 205 all the way across and it has spark to every cylinder.. What can it be??