Brabham Carb Fuel Leakage

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Brabham Carb Fuel Leakage

Postby OUL 735 L » Sat Dec 29, 2018 8:16 pm

Good evening all

Tried starting 1256 engine for the 1st time in over 4 years, but gave up after a couple of minutes due to petrol leaking from the bottom of both carbs. (Brabham carbs and manifold)

Think they are early cd150s as they have smooth brass finish to the bottom, (not Castle type nut).

I read a thread from around 2 years ago saying possible O ring failure.

If i purchase 2 rebuild kits from ebay £17, I assume they will have the correct O rings.

My question is??? if the piston and diaphram are removed is it possible to replace the O rings from the top or will the bottom require removal to replace the O ring,

Any help gratefully received

Regards Ian
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Re: Brabham Carb Fuel Leakage

Postby ADRIAN » Sun Dec 30, 2018 3:43 pm

The whole jet assembly at the bottom has to be unscrewed and removed (with a 17mm spanner if my memory is right.) Fine thread on the assembly so care must be taken on reassembly to not cross thread. When removed, the Inner jet unit, with it spring and a thin washer should fall out behind the main body. (The needle remains as this is in the piston body above) The inner jet has a small "O" ring inside - and the main brass body has a large "O" ring on the outer rim. It is usually the larger one that breaks/cracks & leaks. The original "O" rings from Stromberg were a soft rubber and provide a good seal, but the modern O rings are more plastic and harder, and they dont last long. Especially bad when these have to cope with modern Ethanol in the petrol. I know because I've changed mine many times over ! Always best to get Genuine "O" rings in a kit if you can, rather than just standard O rings. The mixture settings usually have to be re-adjusted again, and the carbs syncronised to work together again, once the jets have been disturbed / removed.
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Re: Brabham Carb Fuel Leakage

Postby OUL 735 L » Sun Dec 30, 2018 4:54 pm

Thanks for the reply

Wishful thinking, hopeing not to remove carbs and manifold from the engine.

Picture below, is it possible to remove this type without disturbing the bottom cover.
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Re: Brabham Carb Fuel Leakage

Postby ADRIAN » Sun Dec 30, 2018 7:38 pm

Thats a late type emission control carb - it is totally sealed at the base, and therefore it cannot be leaking from the main jets O ring.
This type of carb is not the type fitted to a true Brabham Viva. Where is the carb leaking from? I guess that it is leaking out of the overflow, which is due to "either" the float plastic is punctured, so this lets fuel inside the float and therefore the float doesnt float, - not floating UP to push on the needle valve to turn off the "in" flow,
OR the needle jet itself, which is the jet which shuts off/on by the float rising & falling, it may be clogged up or worn, so extra fuel enters the float chamber and excess overflows out of the top at the exit point.
Just like the overflow on your toilet !
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Re: Brabham Carb Fuel Leakage

Postby OUL 735 L » Sun Dec 30, 2018 10:02 pm

Thanks for the advice, you probably correct

Been on youtube, couple of videos explaining how to to service bottom end

had a look on ebay two kits with valve £20 each,

The carbs going on a HC so not worried about being correct items as not many people will know the difference, including myself
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Re: Brabham Carb Fuel Leakage

Postby Fred Dukes » Tue Jan 01, 2019 12:07 pm

I would go with Adrian on the diagnosis - I would get the carbs professionally refurbed and save a lot of heart ache :roll: I have just been sorting out some CD 150 parts to make up a good working carb and the variation in bits drives you bonkers - different adjusting tubes - different bowls - even different size bracket and clip to hold the choke cable outer :roll:
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