changed head gasket on my rs turbo, but the only differnce i done was put another inlet and dizzy on from another engine,

the car struggles to start and when it does it missing like mad

ive checked the timing thats bang on the plugs on rear are in right position, HT leads are new and so is the rotar arm, cap looks in good condition.
and there is fuel in the car and deffo getting to the plugs!

i think i might be dizzy whats the symtoms?