Zenith Stromberg Carbs

[77_MG_Midget]

Can anyone explain what is the purpose of the oil dampener on the carb? I've yet to find a good explaination on why the carb needs a dampener. Thanks!

 

[AltaKnight]

I'm no expert but I've fiddled with my ZS's a bit.
My understanding is that the dampers function is to slow down the opening and closing of the air valve.
Idea being that if it opens too quickly it will lean out the mixture in that intitial second or so before the venturi effect drags more fuel in, the result being a stalling or hesitating engine.
I think it has a similar effect to the carb throttle pump on other types of carbs that gives a quick spurt of fuel right down the throat when you hit the gas.
There are some real carb experts on this board. I'm sure they will respond with a better or more accurate explanation than this.

 

[Geo Hahn]

And because the oil creates the dampening by restraining movement of the piston (air valve) the weight of the oil selected changes the amount of dampening... e.g. heavier oil causes a slower reaction of the piston to an opening throttle.

The effect of the dampening is mainly relevant during acceleration.

[Note: I'm not a carb expert either, so my comments also open to correction or clarification]

 

[sparkydave]

Hi there! The others are correct, it controls how quickly the air piston rises, so when you open the throttle, it will briefly create a richer fuel mixture. It is analogous to the accelerator pump on carburetors you would find on an American car. Here's a link that has some good information on the Z-S carburetor too https://www.chicagolandmgclub.com/techtips/general/generaltips.html. If your damper oil gets low, your acceleration won't be great, and I have found on my own car that it may make the engine hard to start. Under this condition, when the engine catches, the air piston will rise up quickly and the engine may stall. Another little piece of info is that pumping the throttle does not help in starting, because it won't pump extra gas into the manifold the way an accelerator pump would.

-Dave

 

[77_MG_Midget]

Thanks everyone for the posts. It's starting to make sense now... LOL....

 

[77MidgetMkIV]

I also thank you- I too have a 77 Midget with the ZS, and though it is currently operating fine (knock on wood), this post helped me understand a little better. /ubbthreads/images/graemlins/cheers.gif

 

[Thor]

When you open up the ZS carb you will also see a large spring in the top assembly. This spring along with the damper oil work together to cause a delay in the raising of the piston and thus avoid the leaning out of the mixture too quickly when the throttle is opened quickly.

The concept and design of these types of carbs are interesting and you may gain some useful knowledge by getting hold of "How to build & power tune SU Carburettors by Des Hammill". The ZS and SU carbs are based on the same theory and understanding one or the other will give you an advantage in getting the car to run at peak performance/economy.