2.0 carb dohc off a cylinder!

i have a 2.0 dohc carbed sierra. It is off cylinder 4, closest to the gearbox, i have just replaced the spark plug leads and plugs and this has not helped. any one know what could cause this?

''It is off cylinder 4'' im not sure what your question is

sorry i mean that the cylinder is not firing. the cyclinder nearest the gearbox

what year & mileage

dohc glx 2.0 with standard weber 2v tld carb, think its 1990. sorry dont know the miles engine was swapped. i would add that it does not idle very well. there is oil coming from the back of the engine between the head and the block. however the water and oil are not mixing

I would check for a broken valve spring or a worn lobe on the cam shaft. Check compression in this cylinder.