i've just bought a 89' Sapphire Cosworth, currently running at 415bhp. It is misfiring from 4000rpm, i am going to change the leads and plugs. what is the correct gap for the plugs? also gonna check the fuel pump cos it might be starving the engine. also have a oil leak which looks like it is coming from the rear of the engine bay, the oil pressure is fine. gonna check the sump and gear box. if anyone can help it would be much appreciated.

Paul