Carburretor Jet

An article in the recent ‘Chassis’ magazine, published by the Essex Austin Seven Club reminded me of some information given out at one of our ‘Teach-ins’, when members were informed about the small hidden jet which effects the slow running of engines 

Austin Seven owners, using the Zenith 26VA carburettor and suffering from poor, erratic engine idling can now improve the situation with very little effort.


carb jet 11
If you look at the underside of the 26VA you will notice a brass screw head in a raised rib about 30 mm back from the manifold flange. This has always been considered in the past as a blanking screw coving a passageway within the body of the carburettor. This screw plug is, however, an access cover to a jet underneath.

Apparently this jet 'bleeds' a small amount of air into the throat of the carburettor when the butterfly flap is fully closed. If you hold up the carburettor and look into the throat from the manifold end you will see two small holes. The furthest one of these is the entrance to the jet which can easily become choked with dirt and leads to the rough idling. It can be reached by taking out the blanking plug and with a good quality screwdriver which is able to reach far into the hole the jet can be unscrewed for cleaning.  Do use a good screwdriver as the jet is easily damaged.

carb jet 12

You will be amazed the difference cleaning this jet will make. Another useful tip in association with this jet is to have your car ‘gas analysed’ on a Crypton tuner or similar. You will then be able to set the air bleed screw on top of the carburettor accurately. Note the setting by counting the number of turns out, of the air screw, that gives the accurate setting and always use this setting.




Author unknown, but a member of CA7C.


See also:

Carburettor Compensation

Carburettor Throttle Spindles