HS Type Carburetter: Tuning Multi-Carbs
1
(a) Slacken both clamping bolts (1) on the throttle spindle interconnections.
(b) Slacken both clamping bolts (2) on the cold start interconnections.
2
Using a balancing meter in accordance with the maker's instructions, balance the carburetters by altering the
throttle adjusting screws 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.
3
(a) Turn the jet adjusting nut/screw (3) on each carburetter down/clockwise to enrich or up/anti-clockwise to
weaken, by the same amount until the fastest speed is indicated; turn each nut/screw up/anticlockwise
until the engine speed just commences to fall. Turn each screw very slowly down/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 on page 39).
(b) Check the idle speed and readjust it as necessary with the throttle adjusting screws (4), turning each by the
same amount.
4
(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 nuts/screws by the minimum amount necessary to bring the readings just within the limits.
If an adjustment exceeding three flats/half a turn is required to achieve this, the carburetters must be
removed and serviced.
(b) Set the throttle interconnection clamping levers (5), 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.
5
(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 (6).
(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.
(d) Using the balancing meter or listening tube to ensure equal adjustment, turn the fast idle adjusting screws
(7) to give the correct fast-idle speed.
(e) Refit the air cleaners.