One more little job completed today. A semi-circular shaped hole was cut out in the top of the airbox and one half of a piece of hinge match drilled to its straight forward edge. Then an aluminium flap was created to completely fill the normal entrance to the airbox when at right angles to the airbox top. This took lots of iterations of filing and testing to exactly fit the shape of the fibre-glass bottom of the airbox. Once this was a good fit it was match drilled to the other side of the hinge. The holes were then deburred and dimpled to take countersunk rivets. These were set so that the flush surface is inside the airbox to provide minimal disturbance to the airflow when in the normal open position. Then an actuator arm was rivetted to the top of the flap and drilled for a cable connection. The top of the airbox was then bolted to the carburettor and the actuator cable measured and cut. The system is designed so that the cable pull holds the flap open against the airflow when carb heat is required. In the normal closed position the control is fully forward and the cable is assisted by the airflow to keep the flap tight to the top of the airbox and allow the cold air into the carburettor. The hot air intake is mounted over the semi-circular cut out and is spaced off it to allow the heated air to spill into the cowl when carb heat is not required. When heat is required the suction of the carburettor will ensure hot air enter the airbox. The six tabs on the underside of the airbox top-plate hold the K&N filter in position.
One more little job completed today. A semi-circular shaped hole was cut out in the top of the airbox and one half of a piece of hinge match drilled to its straight forward edge. Then an aluminium flap was created to completely fill the normal entrance to the airbox when at right angles to the airbox top. This took lots of iterations of filing and testing to exactly fit the shape of the fibre-glass bottom of the airbox. Once this was a good fit it was match drilled to the other side of the hinge. The holes were then deburred and dimpled to take countersunk rivets. These were set so that the flush surface is inside the airbox to provide minimal disturbance to the airflow when in the normal open position. Then an actuator arm was rivetted to the top of the flap and drilled for a cable connection. The top of the airbox was then bolted to the carburettor and the actuator cable measured and cut. The system is designed so that the cable pull holds the flap open against the airflow when carb heat is required. In the normal closed position the control is fully forward and the cable is assisted by the airflow to keep the flap tight to the top of the airbox and allow the cold air into the carburettor. The hot air intake is mounted over the semi-circular cut out and is spaced off it to allow the heated air to spill into the cowl when carb heat is not required. When heat is required the suction of the carburettor will ensure hot air enter the airbox. The six tabs on the underside of the airbox top-plate hold the K&N filter in position. 
