Need 34 dmsa diaphragms WTB?

[htchevyii]

I've got my carb guru going thru my weber 34 dmsa and he said it needs new fast idle and choke pull off diaphragms . None of the Fiat vendors seem to have them and I don't see them on pierce manifolds, redline weber or weber carbs direct. Any ideas?
Thanks!

[dmwhiteoak]

Did you rebuildThis carb? I have one that needs a kit installed and haven't found one that was reasonably priced.

[htchevyii]

He is rebuilding it now. I'm wondering if the fast idle and pull off can be eliminated? I don't really understand why they are needed on a carb with a manual choke cable? The basic kit is easy to locate for 30-40 bucks.

[dmwhiteoak]

I will continue to look.

[squealingtires]

I too am in need of the fast-idle and the choke pull-off diaphragms. I too have not been able to source either of these. Any help is much appreciated.

[131]

http://www.ebay.com.au/sch/i.html?_from ... cat=131090

[bradartigue]

He is rebuilding it now. I'm wondering if the fast idle and pull off can be eliminated? I don't really understand why they are needed on a carb with a manual choke cable? The basic kit is easy to locate for 30-40 bucks.

Well, no, you don't need them. The fast idle - if it even works - was designed to keep the throttle plate open while decelerator with the clutch engaged in 3rd or 4th gears. Most were bypassed or ignored years ago; the ones that work do a good job of keeping deceleration popping down. But it is not necessary and was only installed on USA cars. It can be capped at the carburetor or removed and sealed. The clutch pull off diaphragm can also be removed, although I'm surprised you have a leak there. I'm actually surprised either leak.

[fiatfactory]

.

[bradartigue]

Fast idle isn't really needed unless the car has air cond, then it's a good idea to keep it.

SteveC

USA cars don't use fast idle for A/C, it was for an emissions control device linked to the position of the clutch and the engaged gear.

You guys drive with the choke "on" ? In that case yes, you need the diaphragm.

[squealingtires]

Thanks for all the help everyone. I found this manual online. Seems like the choke-pull off does exactly what it sounds like and confirms the responses in the thread. So basically as soon as the engine starts (with the choke closed) the vacuum will exceed the diaphragm/spring threshold and the lever will crack the choke open so the engine can get some air.

So my fast-idle diaphragm doesn't need to be in very good shape is what I'm gathering from everyone. From the manual it does come into play during staring but what is the purpose at that stage? If there was enough vacuum then I guess it could help crack-the throttle open. Its been mentioned that it is activated when in 3rd and forth with the clutch engaged. Is there a solenoid attached the vacuum line that opens during this stage? Just learning?

http://www.artigue.com/fiatcontent/carbs/34_DMS.pdf

[bradartigue]

Fast idle doesn't have anything to do with startup or cold running. It is designed to keep engine speed up when the car is decelerating with the clutch engaged in 3rd or 4th gear. It is a USA only device and is intended to help the engine burn fuel that would otherwise go into the exhaust unburnt.

A transmission switch is activated when the car is in 3rd or 4th gear. A switch on the clutch pedal is activated when the clutch is released. When both of these switches are activated an electrovalve opens and manifold pressure pulls against a diaphragm in the fast idle module on the carburetor, which in turn pulls the throttle control and opens the throttle. A switch near the electrovalve allows the owner to set the engine speed at which the throttle is held, which IIRC is 1600 RPM.

[bradartigue]

Fast idle doesn't have anything to do with startup or cold running. It is designed to keep engine speed up when the car is decelerating with the clutch engaged in 3rd or 4th gear. It is a USA only device and is intended to help the engine burn fuel that would otherwise go into the exhaust unburnt.

A transmission switch is activated when the car is in 3rd or 4th gear. A switch on the clutch pedal is activated when the clutch is released. When both of these switches are activated an electrovalve opens and manifold pressure pulls against a diaphragm in the fast idle module on the carburetor, which in turn pulls the throttle control and opens the throttle. A switch near the electrovalve allows the owner to set the engine speed at which the throttle is held, which IIRC is 1600 RPM.

[fiatfactory]

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