Help Please Small Puff like backfire

Please help me i was changing brakes and when i finished all of the
sudden when i start off i get a sound like back fire until I get up to speed
i have had the timing checked its ok, i've replaced plugs rotor and cap
also wires.
I have checked the check engine and all i get is 55
oh yeah and have changed the fuel filter
none of these changes have fixed the problem
Any Suggestions would help alot