Mk3 commando carbs

Andrew Jago · Jul 5, 2022

A question concerning mk1 concentrics fitted to 1977 mk3 commando.
Should screw in pilot jets be fitted ? (the ones that screw up into the body from the float chamber). I know all the tech docs suggest that they should not be there, and that the pilot jet is in the casing behind the adjusting screw, (which they are). But I seem to have a recollection that pilot jets (#25) were fitted. Any ideas

L.A.B. · Jul 5, 2022

Andrew Jago said:
Should screw in pilot jets be fitted ? (the ones that screw up into the body from the float chamber).

No.

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

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Notes On Rebuilding the Amal Mark 1 Concentric Carburetter | AMAL | AMAL Carburetters

The Notes On Rebuilding the Amal Mark 1 Concentric Carburetter page for the AMAL Carburetters website.

amalcarb.co.uk

"Pilot Jets

When first introduced, all carburetters were fitted with a detachable pilot jet screwed into a threaded hole in the bottom of the carburetter body. This arrangement is retained for 2 strokes, but from 1968, was replaced for 4 strokes by a bush pressed into the gallery behind the pilot air screw.
The detachable pilot jet caused problems with some 4 Stroke engines. The remoteness of the jet from the two pilot circuit outlet holes, caused starting and idling problems on bikes with lower manifold vacuums. This could cause stalling during deceleration, due to a weak mixture. The introduction of the pilot bush moved the pilot jet nearer to the outlet holes, overcoming this problem. The bush has a flow rate, equivalent to 20cc/min. Carburetters fitted with a bush, retain the threads originally used to fit the removable pilot jet."

Andrew Jago · Jul 5, 2022

L.A.B. said:
No.

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

Notes On Rebuilding the Amal Mark 1 Concentric Carburetter | AMAL | AMAL Carburetters

The Notes On Rebuilding the Amal Mark 1 Concentric Carburetter page for the AMAL Carburetters website.

amalcarb.co.uk

"Pilot Jets

When first introduced, all carburetters were fitted with a detachable pilot jet screwed into a threaded hole in the bottom of the carburetter body. This arrangement is retained for 2 strokes, but from 1968, was replaced for 4 strokes by a bush pressed into the gallery behind the pilot air screw.
The detachable pilot jet caused problems with some 4 Stroke engines. The remoteness of the jet from the two pilot circuit outlet holes, caused starting and idling problems on bikes with lower manifold vacuums. This could cause stalling during deceleration, due to a weak mixture. The introduction of the pilot bush moved the pilot jet nearer to the outlet holes, overcoming this problem. The bush has a flow rate, equivalent to 20cc/min. Carburetters fitted with a bush, retain the threads originally used to fit the removable pilot jet."

Excellent, thank you

chaztuna · Jul 8, 2022

Andrew Jago said:
A question concerning mk1 concentrics fitted to 1977 mk3 commando.
Should screw in pilot jets be fitted ? (the ones that screw up into the body from the float chamber). I know all the tech docs suggest that they should not be there, and that the pilot jet is in the casing behind the adjusting screw, (which they are). But I seem to have a recollection that pilot jets (#25) were fitted. Any ideas

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850 MkIII Shop Manual & Parts Catalog Errors (2017)

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Mk3 commando carbs

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"Pilot Jets​

"Pilot Jets​

"Pilot Jets

"Pilot Jets