Hi All,

My original post did not go through. So giving this a try.

Have a Zenith 35/40 dual carb setup in my 1967 250S. I know that the diaphragm in the fuel return valve assembly is leaking because of pinholes because I pressure tested the diaphragm.

I have not seen any posts here on how to either seal the pinholes? Or, how disable the fuel return function by forcing the needle/piston in the closed (pushed up).

The pinholes cause gas to leak from the assembly anytime the engine is on.

Thanks in advance.

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250

Am now considering loading the bottom chamber full of Permatex 85420 fuel resistant sealant. This would force the needle/piston in the closed position and keep fuel from dribbling out the bottom of the assembly. And this sealant could be removed in future (unlike plugging it with JBweld, for example).

I can't imagine that a failed diaphragm is that uncommon.

Any ideas, anyone?

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250

karshack, although I am unfamiliar with the fuel return valve on your automobile the only repair that makes sense would be to replace the faulty diaphragm, or the entire fuel return valve if the diaphragm is not available separately.

__________________
Fred Hoelzle

When it comes to the fuel system it is always better to not redesign it.The return is there maybe to keep fuel cooler and not perculate on hot days.Benz should have those available.
Rich

__________________
88 300E White, sold 9-04
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92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car

Thanks Rich. Indeed, from my readings avoiding fuel vapor issues is the principal reason for the fuel return valve. Fortunately, I'm in a part of the SF Bay area that does not get wicked hot often. Maybe 10 days tops, if that. And, it's been ages since I've been in frightfully long lines to get into Laguna Seca or Sears Point.

No, in the short-term I need to stop this fuel leaking. If I need to get a new/old carb (about $200-300) that can wait.

Unless, I hear better ideas I'll go the plug-n-plod route.

Still open to ideas. Thanks!

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250

Hi Ferdman,

I've looked at a lot of carb rebuild/maintenance kits for the 35/40. None of them include this needle/piston with diaphragm. Nearly everything else but this.

I think I would have to buy an entire primary carb. Or, hope to find some pne who is selling individual parts of a primary carb. I do not see how the carb can possibly function without the valve assembly in place. But it can, from what I've read run even if the return feature is rendered inoperable.

Thanks

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250

OTB: Sorry for the delay. Took ages yo find that parts catalog.
Catalog Number 10-107
Mercedes-Benz Type M108
Edition A

Table 5, Groupe 7, Page 28 only shows the whole carburetor no exploded views of parts.
However Page 28 just "Fuel by-pass valve" as part 00-070-11-46.

I would suggest that you contact the Refactory and see if they can help you. If not, contact the folks at Mercedes-Benz Classic in Southern California 1-866-622-5277 or email them at classicparts@mbusa.com.

The reason to not diy this job is that failure probably results in fuel dripping from the carb to hot headers. Pennywise and pound foolish.

Good luck

Thank you, karshack.
I appreciate and accept your advise and as I feel, "A word to the wise should be sufficient"
R/
OTB