I have had my heads professionally overhauled but have now discovered that there are leaks from the combustion chambers into the ports - all of them! I have confirmed this by the old trick of filling the inverted combustion chamber with petrol and checking for leakage into the ports. However, the overhaul involved fitting both new valve seats and new valves, so the leakage could be through the valve/seat interface or through the seat/head interface - or both. Can anyone suggest a test which will determine at which interface the leakage is occurring?