Norton Commando Workshop Manual

## Carburetor

# E

13 | Place the air valve guide tube and spring over the air cable (the brass guide assembles with the flanged end towards the cap).
14 | Compress the spring to expose the maximum of inner cable then pass the nipple through the air valve to engage at the bottom.
15 | Place the throttle valve spring over the throttle cable and compress it.
16 | Feed the throttle cable nipple through the throttle valve centre hole then engage the nipple in the adjacent hole.
17 | Fit the needle clip to the correct groove.
18 | Compress the throttle spring to clear the throttle valve then place the needle and clip into the throttle valve from the top with the needle in the centre hole of the slide. Release the throttle spring and ensure that the spring fits over the needle clip.
19 | Locate the air valve into the channel of the throttle valve. The carburetors with manifolds are ready to refit to the cylinder head. Proceed as follows:
20 | Offer the throttle and air valves, assembled to the cables and tops to both instruments. Ensure that the throttle needle passes easily through centre hole of the body and that the key on the throttle valve mates with the keyway in the carburetor body. Ensure that the return spring fits over the abutment in the top.
21 | Secure each carburetor top with two cross headed screws and washers.
22 | Mount the carburetors on the cylinder head using the heat insulators between the manifolds and cylinder head. Secure with socket screws and washers.
23 | Reconnect the fuel pipes to both petrol taps.
24 | Fit both carburetors to the airbox flexible connectors and take great care that these locate both in the airbox front plate and over the carburetor intakes.
25 | Reassembly is now complete and slack should be taken up in the control cables and the carburation adjusted as in Section E7.

### SECTION E6

### FUEL TAPS

Twin taps are fitted. The one on the right side provides the reserve supply and is recognised by the lack of a stand pipe inside the tank. Fibre washers seal the taps to the tank and must be checked that they are undamaged before being re-used.

### SECTION E7

### CARBURETOR ADJUSTMENT

Adjustment should be carried out in the sequence described below with the engine at operating temperature. The exhaust system to be used must be fitted and preferably the test should be carried out on a slight up grade so that the engine is pulling. The air lever must be fully to the tight wire position before adjustment takes place.
1. Main Jet - Throttle threequarters to full open.
If at full throttle, the engine runs "heavily" the main jet is set too large. If by slightly closing the throttle valve, the engine power seems to improve, the main jet is too small. With a main jet of the correct size the engine should run evenly, and be delivering maximum power at full throttle.
The appearance of the sparking plug is one of the best indications of mixture strength. To check, set the carburetors to shut off completely on closing or false readings will be obtained, then run the machine at full throttle over the test course, declutching and stopping the engine quickly. Then examine the spark plugs. If the plugs have a cool appearance with the central insulator frce from loose black carbon and a light chocolate colour on the insulator, the mixture is correct. A rich mixture will be indicated by a black, wet oily appearance with deposits on the central insulator. Weak mixture will be indicated by a dry whitish deposit and the points may appear to have been overheated.
2. The Pilot Jet - Throttle up to one-eighth open.
Set the engine to run at a fast idling speed with the throttle shut by using the throttle adjusting screw. Turn this screw outwards until the engine runs slower and begins to falter, then screw the pilot air adjusting screw in or out to make the engine run more evenly and faster. If the idling speed is still too fast reduce it by means of

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