Fuel leak from carb

[Duncan Grimmond]

M7 (as with M9 and M11) is something of a "bastard" thread as it is on the cusp of fine to not so fine pitch thread. All three are used quite extensively on 2CV motors and gearboxes as they allow for a smaller boss and reduce weight, very much favoured by M. Boulanger in his 2CV design. He must have saved quite a few grammes like that and somewhat more safely than drilling holes in everything à la Chapman (should that be au Chapman?).

[Ian Wegg]

The latest update to this topic:  I've now discovered that the carburettor has a crack where the banjo bolt screws in. I really should have noticed it before but in my defence, it's on the manifold side and not immediately visible. Of course, it's also possible the crack is new and was caused by my previous attempts at fixing the problem.



I have approached a local precision welding company to see if they can assist but so far they haven't responded. Is this another common problem? Does anyone have any suggestions for fixing this or is it time to just go with my earlier plan of fitting an SU?

[Ivor Hawkins]

I think it might be easier to buy another carb, but if you want to save it I would carefully vee cut the crack and pop in some JB Weld or repair with a two pack epoxy, but it may well be prone to cracking again...

[dickie65]

My suggestion is to clean the carb thread and glue in a pipe fitting like the one on the petrol pump body.
This would mean making a new fuel line to do away with the banjo fitting.
The carb body is a Mazac casting which has a very low melting point !!!

[Jeff Taylor]

A guy called Nigel Hussey is selling one on the Facebook 'Austin 7 Spares / Cars for sale Group' page - he's open to sensible offers. It's apparently missing the slow running adjustment screw.

https://www.facebook.com/groups/44686519...&ref=notif



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[Ian Wegg]

Thanks for the replies.

Glueing in a pipe fitting is something I had thought about and getting rid of the banjo connection altogether is quite appealing! I've seen the Zenith on Faceboook, the owner is now asking £50 for it, which is a fair price if the carb is OK but a bit risky.

I called Tony Betts yesterday and he has the 90-degree converter at a very good price and is going to see if he has a suitable carb to fit, so I plan to call it a day on Zenith and go that route. I know where I am with SUs.

Thankyou again for the continued help.

[Dave Mann]

From the number of mazak 22FZB carburetors I've seen with broken slow running jet housings with the bit unsuccessfully glued back on with various epoxy glues I came to the conclusion that repairing mazak with epoxy glue in the presence of petrol is a non starter. Welding or other such methods usually ends up with a molten mess. What is needed is an engineering solution which with the 22 FZB was to machine the housing off and make a new steel one. I once bought two 22FZB carburetors with broken slow running jet housings at Beaulieu being sold as a source of spares at £5.00 each, both are now giving sterling service. This only works if the mazak isn't suffering from mazak disease where it just crumbles away.

[AustinWood]

I fixed the leak in a plastic bath by running superglue into the crack. Surface tension sucked it in. The plastic was backed by chipboard. It withstood hot water and the weight of someone showering. Don't know how it stands up to petrol though.
To digress, Citroen used to love M7, head is 11mm. There are more M7s on the Citroen SM than any other thread. A bit difficult to get nowadays. Not as bad as the M9 they used for attaching the gearbox to the engine. They are unobtainable new. The only one I found with an internet search was a special bolt used on Lambretta exhausts.
Fortunately I was able to do a swap of bolts for some tappet shims.
I phoned Barry, the SM specialist, and he just happened to have the bolts I needed in his hand having just removed them from a Citroen DS.

[Ian Wegg]

Just a brief update on this thread (I nearly said my thread but I didn't start it, I hope the original poster fixed his problem!)

Sadly I heard nothing more about the SU so I have replaced the Zenith. I bought connectors from Demon-Tweeks and joined them with a rubber fuel pipe:





Both connectors fitted with no issues or leaks so this appears to be a workable solution. Assuming all is well I'll buy some proper braided hose and clips!

In the meantime, I have now found another Zenith which I should have by Wednesday so I have a backup plan.

I'm left with the question, why is a banjo union used on the carburettor at all and not just the same connection as the fuel pump?

[Reckless Rat]

Probably to keep the fuel pipe away from the manifold.