MG MGB TOURER GHN5 Handbook page 71

5. Raise each carburetter piston lifting pin (3), release the pin and check that
the piston falls freely onto the bridge of the carburetter, indicated by a
distinct metallic click. Consult your Distributor or Dealer if the piston fails
to fall freely.
6. Connect a reliable tachometer.
Select 'P' on Automatic transmission models.
7. Start the engine and run it at a fast idle speed until it attains normal running
temperature, then run it for a further five minutes.
8. Increase the engine speed to 2,500 r.p.m. for 30 seconds.
NOTE.-Tuning can now be commenced. If the adjustments cannot be com-
pleted within three minutes, increase the engine speed to 2,500 r.p.m. for 30
seconds and then continue tuning. Repeat this clearing procedure at three-minute
intervals until tuning is completed.
9. Check the idle speed with a tachometer (see 'GENERAL DATA') and check
the carburetters for balanced air intake using a balance meter.
10. If the balance is not correct, adjust by tuning the throttle adjusting screw (4)
on one of the carburetters. Then adjust the idle speed by turning the throttle
adjusting screw (4) on each carburetter by the same amount until the correct
idle speed is obtained. Recheck the carburetter balance.
Check the throMe shaft pin clearance and adjust if necessary-see para-
graph 15.
If a smooth idle at the correct speed and balance is not obtainable, adjust the
idle speed mixture setting as follows:
11. Stop the engine. Remove each suction chamber and piston, and turn the jet
adjusting nut (5) up until the jets are flush with the bridge (6) of the car-
buretter or as high as possible without exceeding the bridge height. Ensure
that both jets are in the same relative position to the bridge of their respective
carburetters. Turn the jet adjusting nut (5) on each carburetter down two
complete turns. Refit the piston and suction chambers and top up the piston
damper oil levels.
NOTE.-This operation need not be carried out if it is known that the jets
are in the same relative position.
12. Re-start the engine and run it at idle speed.
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