Technical Weber 34 dms

[Tom1991]

Hi... I have recently purchased a fiat 124 for restoration, I'm currently trying to get the engine running but having problems with the carb, it has a weber 34 dms fitted

See attached pic, what is this brass pipe on the carb, is it a vent? Vacuum? Or should it be blocked off.

Any info appreciated
Thanks

 

[bugsymike]

Hi... I have recently purchased a fiat 124 for restoration, I'm currently trying to get the engine running but having problems with the carb, it has a weber 34 dms fitted

See attached pic, what is this brass pipe on the carb, is it a vent? Vacuum? Or should it be blocked off.

Any info appreciated
Thanks

Others may be able to give more specific advice, as I last worked on those sorts around the early 1970s.
However, depending on where the car/carb was being used, as in what emission laws applied may affect what the pipe does.
If there is only the one pipe and it can be blown through coming out near the throttle spindle in the choke tubes/venturi, possibly when throttle opened, then I would suspect it would be emissions related and maybe connected to the engine breather system to allow crankcase fumes to be burnt off by the engine inlet. If so it may have to have a PCV valve in the breather pipe somewhere.
It is unlikely to be a vacuum pipe as to large in my opinion, generally any large vacuum pipe to operate the brake servo is fitted in the inlet manifold it's self.
If there were two pipes connected as in flow and return then some areas had a water cooling/heating set up, although usually from memory this would be on an extra lower flange between carb and manifold.
Once carb is thoroughly cleaned and rebuilt with new gaskets etc. then if that tube is as I suspect is emissions related , then a simple rubber plug may be tried to allow engine to be tested, until correct hose/valve etc. fitted to the breathing system.

 

[124BC1]

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If there is only the one pipe and it can be blown through coming out near the throttle spindle in the choke tubes/venturi, possibly when throttle opened, then I would suspect it would be emissions related and maybe connected to the engine breather system to allow crankcase fumes to be burnt off by the engine inlet. If so it may have to have a PCV valve in the breather pipe somewhere.
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I think "bugsymike" is right in this ^^ part of his reply.

Fiat's had a large engine breather (rubber) hose that goes from a breather housing/oil separator mounted just above the oil filter to a pipe stub under the air filter housing. And while it didn't have a PCV valve in the breather pipe, it did have a 'flame arrestor' (like a spiral wire mesh device) inside the large breather hose. There was also a small plastic pipe that ran from a brass stub on the carb to a connection under the air filter housing beside the main breather hose connection. There was a type of rotary valve on the carb butterfly spindle in the carb. just below this brass stub that Op is asking about - iirc, this valve opened as the throttle was opened to allow engine crankcase emissions to be drawn into the engine and then burned (as "bugsymike" has suggested).

So it would appear that the brass stub on the carb should be connected by a plastic pipe to the small pipe stub which should be present under the air filter housing adjacent to the connection for the main engine breather hose.

 

[bugsymike]

After reading what @124BC1 mentioned I can recall those "spiral wire mesh things" and having to clean them during services around the 1970s.
Ladas (Fiat 124 under license) also had a similar thing in the breather to the air filter.

 

[s130]

I concur with how this should all be connected.

In the Starda Abarth which has two Solex ADDHE Carbs (similar to the Weber DCOE) there is a main crank case venting hose that goes into the main main air box with a flame retarder. Halfway along this main hose is a union with a smaller hose that branches into four hoses one of each going to a vaccum tube/port on each of the four carb barrels.