Norton Commando Workshop Manual

## Carburetor

# E

the throttle adjusting screw and again adjust the pilot air adjusting screw until the idling is satisfactory.
Note: When new or re-assembled carburetors are used, start with pilot screw 1 1/2 turns out from the fully-in position.
3. Throttle Cutaway - Throttle one-eight to one-quarter open.
If, as the machine pulls away from the idling position, there is spitting back from the carburetors, slightly richen the mixture by screwing in the pilot air adjusting screw slightly. If this is not effective, return the screw to its former position and fit a throttle slide with a smaller cutaway. If, with the throttle in this position, the engine ji jerks under load and there is no spitting, either the jet ~ needle is much too high or a throttle slide with a larger cutaway is required to cure richness.
4. Throttle Needle - Throttle one-quarter to three quarters open.
The needle controls a wide range of throttle opening and therefore the acceleration. Placing the needle in the lower position, that is, with the clip in the top groove gives a weaker mixture. Placing the needle in the higher position, that is, with the clip in the bottom groove, richens the mixture. If the mixture is too rich with the needle in the lower position, the needle jet should be replaced and if the needle itself has had a great deal of use replace it also.
5. Pilot Jet
Check again pilot adjustment as the last operation.

### SECTION E8

### ADJUSTMENT FOR ALTITUDE

It is necessary to adjust carburation on a motorcycle operated continuously in altitudes greater than 3,000 feet approximately. Motorcycles as supplied from the factory are already equipped for correct carburation up to 3,000 feet.
The main jet requires a reduction in size of 5 per cent at altitudes between 3,000 and 6,000 feet. Beyond 6,000 feet further reductions of 4 per cent should be made.
Altitude adjustments should only be made if the motorcycle is used permanently at high altitudes. It is not necessary to adjust merely for a journey through mountainous areas.

### SECTION E9

### TWIN CARBURETOR ADJUSTMENT

It is necessary periodically to synchronise the carburetors so that they open and close simultaneously. Start with the handiebars in the centre position so that there is no "pull" on the throttle cable which will interfere with adjustment. Proceed as follows:
1 | Take up any slack in the throttle cables using the = adjuster on the top of each mixing chamber, then tighten the adjuster locknuts.
2 | Start the engine - this must be thoroughly wermed up before adjustment commences.
3 | Follow the main adjustment sequence in Section E7 before setting slow running. It is all-important to have both throttle valves opening simultaneously. To ensure that this is the case, the twist-grip should be set to allow the engine to run fractionally over idling speed. Gently screw in the throttle valves in that position. Return the twist-grip to the closed position so that the engine runs on the throttle stops. Now proceed as follows:
4 | Lift off one spark plug lead and commence setting the carburetor on the other cylinder as a single unit.
5 | Adjust the pilot air screw and stop screw on the cylinder which is firing.
6 | Reverse the process by replacing one plug lead and removing the other.
7 | Adjust the pilot air screw and stop screw on the second cylinder.
8 | Replace the plug lead - at this stage tickover may be too fast. If so, lower both throttle stop screws by an equal amount until idling is correct. Ensure there is. about 1/4" (6 mm) slack in throttle cable. This slack must be equalized so that throttles open together.

### SECTION E10

### AIR FILTER

The airbox comprises a detachable front plate, perforated metal band and replaceable automobile type air filter element, the backplate being mounted directly on to the front of the battery tray.

<< | < | rocbo.net | >