Tuning - Multi

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HIF Type Carburetter: Tuning Multi-Carbs



(a) Slacken both clamping bolts (1) on the throttle spindle interconnections.
(b) Slacken both clamping bolts (2) on the cold start interconnections.



Using a balancing meter in accordance with the maker's instructions, balance the carburetters by altering the throttle adjusting screws (3) until the correct idle speed and balance is achieved. Alternatively, use a 'listening tube' to compare the intensity of the intake hiss on all carburetters and turn the throttle adjusting screws until the hiss is the same.



(a) Turn-the jet adjusting screw (4) on each carburetter clockwise to enrich or anti-clockwise to weaken, by the same amount until the fastest speed is indicated; turn each screw anticlockwise until the engine speed just commences to fall. Turn each screw very slowly clockwise by the minimum amount until the maximum speed is regained. From this setting adjust the mixture screws according to the vehicle manufacturer's recommendations. (See graph in HIF type carburetter: Tuning Single Carbs).
(b) Check the idle speed and readjust it as necessary with the throttle adjusting screws (5), turning each by the same amount.


(a) Vehicles with emission control. Using the exhaust gas analyser, check that the reading is within the limits given in the vehicle manufacturer's tuning data. If the reading falls outside the limits given, reset both the jet adjusting screws by the minimum amount necessary to bring the readings just within the limits.
(b) See the throttle interconnection clamping levers (6), in accordance with the vehicle manufacturer's instructions, so that a clearance exists between the link pin and the lower edge of the fork. Tighten the clamp bolts, ensuring that there is approximately 0.8 mm (1/32 in) end-float on the interconnection rod.
(c) Run the engine at 1,500 r.p.m. and check the throttle linkage for correct connection by rechecking the carburetter balance.


(a) With the fast-idle cams of each carburetter against their respective stops, set the cold start interconnections, so that all cams begin to move simultaneously (7).
(b) With the fast-idle cams against their stops check that a 1.6 mm (1/16 in) free movement of the mixture control (choke) cable exists before the cable moves the cams.
(c) Pull out the mixture control (choke) until the linkage is about to move the jet (8).
(d) Using the balancing meter or listening tube to ensure equal adjustment, turn the fast idle adjusting screws (9) to give the correct fast-idle speed.
(e) Refit the air cleaners.

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