Mystery Plug Revealed

by our ever resourceful friends in the Essex Austin Seven Club.

Article re-printed from their excellent “Chassis” magazine with many thanks

For all those owners of A7s with a side-draught carburettor who are experiencing idling problems when the butterfly is fully closed, even though all visible jets are clean and all correct adjustments have been made, then we have a tip which could mean those days are finally over!

The answer could lie in the fact that there is a hidden jet which does not appear on any diagrams of the carburettor! The question has baffled even the most experienced Sevener over the years but at Roger Spearman’s Masterclass held on Sunday 3rd March Roger showed an intrigued ensemble exactly why many 26VA carburettors are mistakenly thrown away.

Just adjacent to the slow running jet is a brass blanking screw covering the mysterious jet. It turns out 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 you will see two small holes. The furthest one of these is the entrance to the jet which can easily become choked with grunge 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.

After 75 years of the Austin Seven isn’t it good to know there are still some mysteries the old girl keeps?