This is the tubing and one-way valve assembly that allows fumes that may build up in the crankcase as the oil is being sloshed about, to escape. In some cars, the tubing feeds straight back into the air filter housing, but on the Capri, the tube is fed into the inlet manifold. So in effect, the engine re-consumes its own fumes. The tube is found behind the distributor and under the carburettor. Use a torch to see it as it is a bit dark down there. The valve is fixed in a hole on the top of the crankcase. If you pull it, you will find that it lifts away from the engine. The other end of the tube is fixed with spring clip. Once removed, give the valve a good wash in turpentine as it is often clogged up with sticky oil deposits. When cleaned, if you shake it, you should hear the valve rattling. If not, I suggest getting a replacement as this simple thing can make your car 'hesitate'.