Reece Fish Carburettor

Reece Fish Carburettor
Reece Fish Carburettor fitted to BMC A series inlet / exhaust manifold
Overview
Manufacturer	Leonard Reece & Co
Production	1969–1984
Powertrain
Engine	A-series, 850–1275 cc I4

The Reece-Fish carburettor was a carburettor used by Mini Se7en racers in the 60s and 70s.

The original Fish carburettor was developed in the 1930s by US hot-rodder Bob Fish.

The original intention of the Fish carburettor was to avoid the problems of the float chamber, and its sensitivity to sideways forces from acceleration and cornering. In the conventional carburettor, a venturi in the airflow creates a lowered pressure and this is enough to encourage the flow of fuel through the metering jets. The flow rate is critically sensitive to the fuel pressure at the jet, i.e. the hydrostatic head owing to the depth of fuel between the jet and the float level. Any sloshing within the float chamber affected this. Fish's design kept the float chamber, but avoided the dependency of flow rate on fuel depth. The float chamber was sealed and pressurised by a ram air effect from the air inlet, which then caused fuel to flow through the metering jet. This flow rate was entirely independent of fuel level, but did remain approximately proportional to the mass airflow. The Fish carburettor was also sensitive to mass airflow, rather than volume airflow, making it self-compensating for changes due to temperature or altitude.

A second problem with the conventional carburettor was its good performance in steady conditions, but poor progression: its dynamic ability to respond, such as when suddenly opening the throttle. This could give 'flat spots' in performance, or required great additional complexity to the carburettor such as multiple chokes, emulsion tubes and accelerator pumps. The Fish carburettor metered its fuel flow through a calibrated tapered groove, connected directly to the accelerator pedal and the throttle butterfly. The fuel metering orifice was controlled in immediate proportion to the throttle position, in a similar manner to the motorcycle slide carburettor. Between the float chamber and the venturi, an additional chamber, unique to the Fish design, contains the metering arm and groove. The arm is attached to the throttle spindle, moves with it, and is drilled with a hollow channel supplying fuel to the jets on the throttle spindle. This arm has an inlet hole at its end, which is a simple drilling and not of precise size. The hole passes over the metering groove, which is a radial arc in one wall of the chamber and it is the width of this groove which is precisely controlled, so as to accurately meter the fuel. As the throttle arm moves to the wide-throttle position, the arm sweeps across to the wider part of the groove, allowing more fuel to flow. The arm is close-fitting within the width of the chamber. As it moves, this close fit has the effect of a vane pump and acts as an accelerator pump to force additional fuel into the jet when the throttle is first opened.