just fitted new engine in my s2 now it only starts when cold idles ok wont pick up though and on the rare occasion it does it is really lumpy replaced dizzy rotar arm plugs and leads got good spark help

 

sounds like fueling issues buddy, go throught the usual procedure,

check engine temp coolant sensor mainly and other relevant sensors,
check the voltage at your fuel pump,
check that the flap on your metering head is opening on throttle
and if all else fails get it to a tuner to set up the fueling

 

where is the coolant sensor located

 

its the yellow coloured sensor on the bottom of the sandwich plate between the inlet and head mate