The carburetors on all 3 litre BMW engines must have a vent chimney like one shown

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bavbob

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Title is per the [FONT=Arial, Helvetica, sans-serif]Zenith INAT 35/40 carburetor references posted in this forum. [/FONT] Does anyone know what advantage this has over the non-vented form? I have one vented (like below) and one not vented on my 72 E3 (original owner has no idea who did this) and have bypassed all the emissions stuff. I assume venting is a non-issue because of this but have 3 donor carbs so can easily swap the non-vented to vented if need be. Comments welcome.

48.jpg
 
They're all vented, but the one with the extension was on later cars and a recall for the earlier cars. It's meant to dump any overflow fuel from the float bowl into the carb throat instead of overflowing out into the air cleaner and possibly out onto the engine, which could cause a fire.
 
Thanks. Figured it was safety or emissions and nothing to do with performance. Actually had that issue happen.
 
Hi there,
I am also now rebuilding my Zeniths and have the same problem - manual states that all "Tower" type vents must be replaced by Vent Chimneys. Both of my Zeniths have Towers. Any ideas where I could get those? Or should I just forget about that and use the ones I got...
 
I rebuilt the Zeniths for my 2800cs and a short time later found the front carb was spilling gas into the air cleaner and onto the ground. Whoops.
Apparently the gasket set I used wasn't quite right. The gasket is a bit too small and the float catches on it and can't come up to close the needle valve.

It seems like it would be a rare issue ordinarily, but I can see where BMW would be obligated to design out the potential hazards. Once I fix my carbs, I'm not too worried about it happening again.

Ian
 
i had originally towers, rebuilt the carbs 5 years ago using their original towers
no issues so far
IMHO, there is no need to replace, but i can understand what @ben explained, probably correct
 
Ok, thanks for sharing your experiences. Will stick to Towers for now then, while looking for Vent Chimneys, and make sure new gaskets sits perfectly to let float move freely.
P.S. I also wrote to BMW Classics store in Germany for info where to get those chimneys. If something comes up, will share it here.
 
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