cam specs for E303

i have 1.6 r/r.. could that be why im back firing???
it wont do it at WOT, only when i floor it, it back fires then takes off.... i have all kinds of mods with stock injectors.. also im NOT mass air
any ideas??
 
E303 :Single pattern lobe profile

Duration: 282/282 ... 220/220 @ .050

Lift: .498/.498 at valve with 1.6 rocker ... lobe .311/.311

LSA: 110*

Intake @ .050 (opens/closes): 0btdc/40abdc
Exhaust @ .050 (opens/closes): 40bbdc/0atdc

Firing order:1-3-7-2-6-5-4-8