Tuning Carburettors - Triumph Spitfire MK3 Handbook

Tuning Carburettors (Figs. 100 to 104)
Twin carburettor installations cannot be successfully tuned
unless the general conditions of the engine, ignition and the fuel
systems is satisfactory. Before attempting to tune carburettors,
ensure that the engine oil filler cap and the dipstick are both
secure, as air drawn into the crankcase will affect the engine slow
running.
Remove the air cleaners and run the engine until it reaches
normal operating temperature. Slacken the clamping bolts on the
throttle spindle connections (2). Close the throttles fully by un-
screwing the idling adjustment screws (1) and then open by
screwing down the screws one and a half turns.
Remove the suction chambers and pistons. Screw up the jet
adjusting nuts (3) until each jet is flush with the bridge of its car-
burettor, or as near to this as possible. Replace the pistons and
suction chamber assemblies and check that the pistons fall freely.
Turn down the jet adjusting nuts two complete turns (12 flats).
Restart the engine and adjust the throttle adjusting screws (I)
to give the desired idling speed by moving each throttle adjusting
screw an equal amount. Using a length of 0.3" (8 mm.) approx.
bore tubing, listen to the hiss in the intakes and adjust the throttle
adjusting screws until the intensity of the hiss is similar at both
intakes. This will synchronize the throttles.
Set the pins of the throttle interconnecting levers (2) 0.0l5"
(0.4 mm.) from the lower edge of the forks (Fig. 100), ensuring
that there is 312 (0.8 mm.) side play between the interconnecting
levers and the throttle nuts.
RUNNING ADJUSTMENTS
63