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SS100 Build Manual (Export Edition)
Rev 10 November 2013
13.2
Carburetion
13.2.1 Carburettor base settings
Remove the carburettor dashpots by first removing the screw top dampers (lay these down somewhere clean)
then remove the four screws around the dashpots and lift them away along with the dashpot springs below.
Then you can lift out the piston and needle and look at the height of the jet in the bottom of the carburettor, a
good base setting is to have these 1/16-inch under the height of the jet mount. Refer to Haynes manual or
similar for adjusting the jet position as there are too many types to go into detail here. Refit the needle and
piston taking care not to bend the needle and fill the centre tube to 5mm from the top with a thin engine oil,
the springs and dashpots and dampers can now be refitted.
13.2.2 Starting
Reconnect the coil HT 'King' lead, with these base settings your car should now start. Refit the fuel pump
fuse and turn the ignition on, wait for the fuel pump to slow a little indicator fuel has reach the carburettor
float chambers, Check for any leaks and sort now before attempting to start your car. Check your in neutral,
pull out the choke and press the starter button your car should start if not check the above settings again and
spark plug order.
13.2.3 Warm up
Let the engine warm up to running temperature while keeping a close eye on the water system, the water will
most likely drop as air comes out to the radiator, also check the pipes all become warm as the thermostat
opens to show that there is no air lock.
13.2.4 Dwell angle
The best way to check the contact breaker points gap is with dwell angle, this is the length of time that the
points are open, Dwell angle can be tested by many types of electrical meter and on home gas analysers
which are well worth having and easily obtainable for around £100. The dwell angle should read 35° ± 3, If
the dwell angle is too large then switch off the engine before removing the distributor cap and increase the
points gap if it's too small reduce the points gap. The dwell angle on electronic ignition systems is not
adjustable so bypass this section.
13.2.5 Stroboscopic timing
After checking and adjust dwell angle the timing must be set with a stroboscopic timing light, this will
ensure the spark arrives at exactly the right time and must be done before any adjustment to the carburettors.
With the engine switched off highlight the engine timing pointer on the timing chain case and the correct
timing mark on the front pulley, the number marks on the pulley may not go far enough if so measure the 10°
mark and double the gap for 20°.
Connect up your timing light following the manufacturer's instructions, restart your engine and disconnect
your vacuum advance tube to the distributor. With a helper or by locking the throttle cable out hold the
engines revs at the required amount to set your timing (4.2 XK engine is 20° @ 1800rpm with the vacuum
pipe disconnected) and use the timing light to illuminate the timing marks, if not aligning then loosen the
distributor clamp bolt and turn the distributor either way until the marks line up with the timing light.
Once happy the timing is correct tighten the distributor clamp bolt and refit the vacuum advance hose.
13.2.6 Carburettors
Once happy with the distributor timing you can move on to carburettor tuning, Please refer to a manual for
your carbs for accurate information on your carburettors mixture screws etc or if you have HD8 which have
air bleed screws instead of slow running screws. With the engine at running temperature, slacken the pinch
bolts on the throttle linkage to separate the carburettors then look into the carburettor mouth and adjust the
slow running (tick over) adjustment screws so that both carburettors are open the same amount and the tick
over is at the correct (the gap between the bottom of the piston and carburettor should be the same). Once
both carburettors are open the same amount and the tick over is correct, switch off the engine and tighten the
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