Triumph SU CARBURETORS SERVICING AND TUNING

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Filed Under (Triumph) by admin on 29-10-2010

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Jets: These are made in various sizes ranging from.099 inches to.1875 inches, the larger sizes being used only for racing or very high performance engines. The two sizes most commonly found on production cars are the.090 inch and the.100 inch. The size of the jet will be found stamped on the jet head. The figure “nine”wilt indicate that it is the.090 inch and the figure “one”will indicate the.100 inch jet. When tuninga production car the jets size should be checked to make sure that it is of the size recommended by the manufacturers. Centering of Jet: If for any reason, the jet assembly has been removed, it will be ne cessary to recenter the jet. First, remove the clevis pin at the base of the jet which attaches the jet head to the jet operating lever. Withdraw the jet completely and remove the adjusting nut and spring, then replace the adjusting nut, without its spring, and screw it up toits highest position. Slide the Set into position until the jet head is against the base of the adjusting nut. When this has been done, find out if the piston is perfectly free by lifting it up with the finger and allowing it to drop. If the piston is not entirely free, slacken the jet screw and manipulate the lower part of the assembly, including the projecting part of the bottom half of the jet bearing, adjusting nut, and jet head. Make sure that this assembly is now slightly loose. The piston should then rise and fall quite freely as the needle is now able to move the jet into the required central position. The jet screw should now be tightened and a further check made to determine that the piston is still quite free. When complete freedom of the piston is achieved the jet adjusting nut should be removed, together with the jet, and the spring replaced. Experience has shown that a large percentage of carburetors, which have given trouble has been due to the incorrect centering of jets. Jet Needles— These are made in a great variety of sizes, probably now well over two hundred and fifty, and each type of engine hasaneedlethat has been selected, after very careful tests have been carried out, to give the best all-round performance. Most manufacturers actually give three alternative needles for each type and size of engine, these needles clearly being listed by the manufacturer “Standard”, “Rich”or”Weak”and before tuning is started the needle, which is marked on the shank should be checked against the manufacturer’srecommendation to make quite sure that the right needle is fitted; this is most important.