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Weber DCOE 40 fuel leak

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Alex Staidle
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Weber DCOE 40 fuel leak
November 23, 2017 09:41PM
freshly rebuilt M10 bmw motor. Dual DCOE 40s. Supposedly rebuilt before we put them on the car. So after idling for not that long, fuel seem to come out of the front of the horn on cylinder 4, and front between the o-rings, on cylinder 2. Doesn't seem an issue on 1 and 3. Fuel level appears to be fine. If i pull the horn out there is fuel between the body of the carb and the aux. venturi.

So I had been discussing this with John. I understand that they do leak a little but this seems to be a concerning amount. because i can just watch it drip while running. I adjusted the plate to make sure vacuum wasn't excessive but doesn't seem to be an issue.

also, the idle mixture screw on cylinder 1 will change engine speed. Not so much on 2, 3, and 4.

Short of attempt to rebuild these things, any other thoughts?



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hoche
Michel Hoche-Mong
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Re: Weber DCOE 40 fuel leak
November 24, 2017 02:31PM
Bring 'em here. I like rebuilding carbs.



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Rx7Kevin
Kevin Schmidt
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Re: Weber DCOE 40 fuel leak
November 28, 2017 09:02AM
When you crack the throttle does the engine die? or at least the 2 cyl's fed by that carb? sounds like a sticking float.



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Alex Staidle
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Re: Weber DCOE 40 fuel leak
November 28, 2017 10:14AM
nope, keeps running. Car drives fine. I verified the floating was not overfilling as well.



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danster
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Re: Weber DCOE 40 fuel leak
November 28, 2017 11:49AM
Difficult to diagnose over t"internet without being able to see the installation firsthand.
I recently rebuilt some DCOEs that had similar issues to what you describe. Absolutely everything stripped out and removed for cleaning and inspection including accelerator pump bypass and choke jets. The owner shat himself when he saw 4 carbs completely stripped to bits on the bench! eye popping smiley
These were 4 identical carb bodies and I selected the best components to make the optimum pair.

Mixture screws not having a noticeable affect to running sounds like it could be a balance problem between the carbs so the engine is mainly running on one carb which is flowing more air, or simply partially blocked idle jets which doesn't take much seeing as the fuel holes in them are around 0.5mm diameter.
Some engines are very fussy about airflow and idle mixtures / jet selection so setting them up takes a bit of finesse and skill.

Are your carbs the early type with the curled flat spring key orientating the auxiliary venturi, or the later type with the grub screw and locknut to clamp the aux vent in the carb body?
Early type can allow the aux vent to rattle around and wear a bit depending on how the trumpets have been fitted.
Fuel mixture doesn't issue through the aux vents at idle so shouldn't be the cause of fuel leaking. However, the later carbs can also have idle air bypass adjustment which is preset at the factory when new. If there is wear or a slight twist on the throttle shaft or someone has played around with the air bypass screws that could account for poor unresponsive running at idle / progression phase.

The accelerator pump jets should have tiny alloy crush washers where they seat in the carb body and are clamped in place by large brass plugs with O rings to seal them. Modern fuel with ethanol content does seem to trash O rings and cause them to leak. Fuel may dribble passed the pump jets if the alloy crush washer is missing or damaged.



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hoche
Michel Hoche-Mong
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Re: Weber DCOE 40 fuel leak
November 28, 2017 04:31PM
My understanding is that the ethanol doesn't affect the o-rings directly; rather it causes the aluminium to corrode and that in turn causes the o-rings to unseat. In other words, you may have to do some cleanup of the metal itself.



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