THE CARBURETTER.

Press, Volume LXI, Issue 18365, 24 April 1925, Page 7

THE CARBURETTER.

SETTING FOR SPEED. HINTS FOR THE OWNER. "While tho majority of motorists, especially those who are new recruits to tho ranks, are content with the speed of their oar, inevitably there comes a time when the desire for a little more speed disturbs their elated but satisfied state of mind. It must be borne in mind that any average touring ear can be urged to do ji few more mil's per hour, and that the carburetter setting fixed by the makers is an rJI-roi'.nil one, i.e., one that strikes a ccmpiciii.i-c between good consumption, smooth acceleration, and reasonable speed. If, however, any of oul- readers are bitten with the desire for more speed on the level and a more exhilarating climb in second ge:-r, these lie within reach, provided he is prepared to use n little more petrol, and to have a car that may not be quite so tractable in traffic on'ton gear. The size of the carburetter ana its setting is an important factor, and the amount of air that can pass through it depends :rlnmst entirely on the size of the choke * tube or venturi tube, as it is sometimes called, tins being the carefully graduated rcfitricthe point where petrol enters the induction system on its way to the engine.

Importance of Choke Area. It is essential that the area of this choke tube is something less than that of any other nrrt of the induction system, otherwise the carburetter will no longer function as an instrument delivering a mixture having a constant l>etTol-air ratio at all engine speeds. The diameter of most choke tubes is marked on them, and it is usually safe to make a start "with an increase in the neighbourhood of about 10 per cent. . The jet or jets will have to be increased in size accordingly. as the effect of fitting a larger choke tube will bo normally to reduce the suction 011 them. The ignition timing can also be slightlv advanced on account ot the higher engine speed obtainable. Having found the correct jets tor the increased size of choko tube, a hirthoi increase all round can be tried, hut this must only be done st*;> by stop and, one size at :i time The effect of fitting a larger choke tube will piobalnv be to increase the difficulty of tuning the carburetter to pick up satisfactorily from a low speed in ton gear aiu. after changing down under load. The size of the choke tube ana jet* cannot bo increased indefinitely, for there will come a, time when the engine is unmanageable, due to the air speed throueh the carburetter and induction nine falling below a certain minimum value found necessary in practice. The loss of smooth acceleration which accompanies the use of an -nersize choke tube is due to the.fact that c.t email throttle openings the air speed past, the jet or oriface, whero the petrol meets the air stream through the carburetter. is too slow to take petrol in sufficient quantities into the engine at verv critical period. The extent to which this alteration i« carried will denend upon the wishes of the individual concerned, and the maker of the particular carburetter (or hi-* agent) will always be found willing to advise any owner as to the probable limit to such an alteration. The production of bricks in Great Britain for the three years prior to tlie war was 2.805.000,000 per annum, according to Mr N. Chjunberlan, At present the rate was about 0000 millions per annum.