BMC Mini 4/25 fuel drain tube missing

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Vagabondrv
Posts: 2
Joined: Sat May 04, 2024 12:07 pm
United States of America

BMC Mini 4/25 fuel drain tube missing

Post by Vagabondrv »

Hello. Recently after brush mowing a tall field, I noticed a hissing sound around the carburetor/intake manifold that I never heard before. I traced it to the bottom of a drilled bolt on the outside edge of the intake manifold. By searching this forum, I see there is supposed to be a small tube inserted into this hollow bolt, and the tube is an overflow drain for the carburetor. Apparently, my tube got ripped off by trees/brush rubbing against the tractor while mowing. I can put my finger over the hole while the engine is running and it is definitely sucking air from engine vacuum. I temporarily plugged it to continue running. Can anyone give insight into the importance of this tube, does it need to be replaced and if so where can get one, or, can it just be plugged off? It Doesn’t make sense to me to leave an open vacuum nor how the tube works as a drain and open to vacuum at the same time. Many thanks for any comments. I have enjoyed reading on this forum
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Nowtnew
Senior Member
Posts: 618
Joined: Sun Apr 01, 2018 8:49 am
Great Britain

Re: BMC Mini 4/25 fuel drain tube missing

Post by Nowtnew »

I think the idea of the drain tube is to prevent liquid fuel entering the engine in the event of a 'flooding' incident with the carburettor. If you can supply a photograph of the 'hollow bolt' we may be able to give further advice. The pipe union might have come unscrewed or the pipe may have snapped off.

Regards

Oh sorry, didn't see the photo, but i'm not sure it shows where the pipe connects.
Ley154
Senior Member
Posts: 251
Joined: Sun Apr 01, 2018 8:22 am
Location: Gloucestershire UK
Great Britain

Re: BMC Mini 4/25 fuel drain tube missing

Post by Ley154 »

The tube is there to drain any fuel that may collect around the hot spot inside the manifold. I have made them in the past from a bolt drilled as in the photo and brazed on a piece of 3/16 brake pipe. The open end was crushed down slightly just to allow drops of fuel out. However I now have a 4/25 with the original pipe intact and I see the tube can be 1/8 dia ( oil pressure gauge pipe) which has a tiny bore. If you have the facilities just make one. John Poulter.
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Vagabondrv
Posts: 2
Joined: Sat May 04, 2024 12:07 pm
United States of America

Re: BMC Mini 4/25 fuel drain tube missing

Post by Vagabondrv »

Many thanks. Will get some 1/8” tube and braze it in the nut accordingly.
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