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A Simple Carburettor Bowl Repair


This article is a re-write of one I prepared in 1999 for the MMM Register “Infoletter”, which I edited for about six years before it was superseded by the rather excellent MMM Bulletin. The carburettor was on my MG PA but this repair would be applicable to any similar SU Carburettor and an appropriate small screwselected.


I was while out on one of my “let’s take Lucky Eddie (my PA) out for half an hours run to give him some exercise” excursions that I noticed that he was not climbing hills to well, certainly not as well as I’ve been accustomed to him doing.


The symptoms were similar to running with the choke half out. A quick look under the bonnet revealed a loose bowl lid on one of the carburettors. A quick gentle tightening with my old 5/16” spanner seemed to do the trick and he went well again so we continued on our way for about an hour and then home. These sort of things you take in your stride don’t you? All part of the fun (at least I think so as long as it ain’t chucking it down with rain at the time although I’ve got soaked on many a occasion).


Nothing more happened for quite a while until one day coming back from a good day out the same thing happened again only this time it wasn’t possible to tighten the bolt that holds the lid on. Needless to say, we got home safely but not as quickly as we usually do.


This time off came the bowl for closer examination, which showed that the ¼” thread at the bottom of the bowl had stripped.There was sufficient thread tore-secure the central rod, even when tapped out further with a blinded tap.There was sufficient to “locate” it so I drilled a small hole right through the bottom of the bowl from the inside Stage 1. To do this I put a small drill into a pin vice and the pin vice into my drill which enabled me to reach the bottom of the bowl. It is vital to get this drilled hole central as you will see later.


Having drilled the pilot hole I screwed the central rod back into the bowl without damaging the remaining thread. I then turned the bowl, with the central rod in position and marked the end of the rod using the pilot to position it centrally (Stage 2).

 Carb. Bowl repair 1


I then took the central rod out and drilled and tapped out a hole 4BA (or M4) 3/8” (10mm) deep in the centre of the rod. The pilot hole in the bottom of the bowl was then opened up to take the screw and countersunk so that the head of the screw as flush with the bottom of the bowl (Stage 3)..


Having thoroughly degreased all parts I screwed the central rod back in position with a little “Araldite” as well as the small countersunk screw (Stage 4). Needless to say it’s now 2015 and still sound.


The diagrams below show the steps.




 Carb. Bowl repair 2  Carb. Bowl repair 3
 Carb. Bowl repair 4  Carb. Bowl repair 5

By John Harris