306 1.4 missfire

[hamish]

hi desperate for advice
i have N plate 1.4 petrol,have just replaced cylinder head after old one cracked
replaced everything reqired ie bolts gasket etc and also cleaned up all valves that were in the 2nd hand head
problem is im still getting a missfire
things ive tried include replacing plugs and leads checking wiring loom connections at passenger headlamp new coil pack

any one any ideas as to what problem can be

thanks