CARBURETTOR TROUBLE

NZ Truth, Issue 1188, 6 September 1928, Page 15

CARBURETTOR TROUBLE

Why There Are Three Jets— and Their Functions QNE of the troubles many motorists experience is that relating to carburetion, and at this season of the year a short talk on the functioning of the carburettor will probably be appreciated;

MOST carburettors consist m reality of three instruments, each of which performs one distinct phase of the work of supplying explosive mixture to the cylinders. . . First, there is a miniature carburettor, consisting of what is termed the "slow running jet" with its separate fuel feed from the float chamber and its own supply of air. This small carburettor comes into operation when the throttle is shut, the remaining jets being inactive, and, m consequence, it Ib this jet that supplies the mixture of fuel and air for starting purposes. The throttle being closed, the suction of the engine is concentrated on an orifice communicating with the slow runner. When the throttle opens, the suction is no longer concenti'ated on this point, and gradually, the slow running jet ceases to function. Just previous to this action another carburettor commences to operate, or perhaps it would be better to say that the second section of the existing carburettor takes up the work. This latter consists of a jet, sometimes called a compensator, arranged so that it is supplied with fuel from a well, and its purpose is to give a rich mixture, for a short period of time as the throttle opens. The engine's powers of act celeration depend upon this jet to a' very great extent. The supply of fuel to the compensator ii so arranged that the engine can suck away fuel when the throttle is open more quickly that the well can fill, which automatically puts the compensator out of action at the correct moment, so that this jet supplies no fuel at all when the car is running at a round speed on the road. The moment the throttle is shut the iiiiiiiiiiiniiiiiniiiiiiiiiiiiiimiiimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiimiiimiiiiiiiimiiiiiiiiii

well fills up again, and the compensator is ready to perform when the car has to accelerate again. Air for the compensator is generally supplied through the main air intake, so the compensator does not function until the. throttle is partly open. Finally, there is the third section of the carburettor, consisting of the main jet regularly supplied with fuel from the float chamber and with air from the main air intake. This jet will cut m while th© compensator ls still supplying fuel, but continues to operate when the compensator well is dry. It is necessary to understand this sequence of operations m order to diagnose any trouble that may occur. It is obvious that if the engine will not start m the morning with the throttle closed, it is the slow running jet, and not the compensator or main jet which is at fault. As th'e slow running jet, as a rule, has the smallest orifice, it is the latter which retains any dirt that lodges near it. : ' ' ! ' " If the engine will start, but the acceleration is bad when the engine is warm accompanied by explosions "within the carburettor, the compensator is the jet at fault. If the engine will start and accelerate, but dies aAvay when the throttle is fully opened, recovering when the throttle is practically closed, obviously the main jet has become blocked with foreign matter. , Supposing the engine will run fast, pull well on hills, and function normally until the throttle is released, bulj stops before the throttle can be opened again, a defect m the slowrunning jet is at once indicated,, with the suggestion that both compensator and main are m good working order. iMiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiliiiiiiiiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiHiiiiiiii