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Billemc

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Howdy folks. I am new to this website. Found it this AM not by accident, I went looking for one. I am on another site with old Ford pickups. I am currently working on two vehicles, a '71 Ford F100, and a '79 Midget. What a contrast. For one I need a ladder, for the other I need to be on my knees.
Here is my problem. I need to know the relationship between the damper piston and the choke. The car will only run if I hold the piston open with something. The choke is not hooked up. Someone in the past life of this little car has done some serious modifications (I use this in lew of a more negative phrase). I guess I am looking to fine out what controls the damper. Any help will be appreciated. I will be looking for help from folks who know about this vehicle while I am attempting to bring it back to life. Thanks in advance for your help. Billemc /ubbthreads/images/graemlins/cheers.gif
 
Hello Billemc,
I am not fmiliar with US spec Midgets but I assume it has either S.U. or Zenith Stromberg carburettors. Both work in the same fashion, they are a variable choke with a single needle and jet. The amount of air being drawn into the engine, i.e. throttle position, determines the piston position. Closed throttle and the piston almost closes and vice versa. (You refer to a damper but i guess you mean the piston. There is a damper within the piston which is the little plastic topped screw on the top of the carburettor.)
If you have to manually lift the piston to get it to run, then it is probably far too weak. So you need to connect the choke to get it to run easily from start. There is no direct link between the choke and the piston.
If you still have problems then you probably need to set the carburettor(s) to the basic set up. S.U.'s I can help with but Strombergs I do not have the information.
good luck,
Alec
 
Thanks, it is a Strumburg. There was a rigged up manual choke on but what didn't fall off I removed. I have seen some manual choke conversions but they are very pricey. I am thinking more and more that the choke is the problem, now all that is need is to figure out how to fix it. Billemc
 
Welcome Bill!
One of the most common problem on the ZS carb used on your car is a worn-out diagphram.
When these crack or tear with age, the piston will not move up and down properly, causing poor running. You can buy one from Moss for about $6.00 USD or buy and entire carb-kit for about $25.00. The diagphram can be seen as part # 2 on this page.

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29283

You may also want to make sure there is no dirt in the float bowl (another common problem).
By the way, the piston is not connected to the throttle directly. When you open the throttle (step on the gas), more air is drawn into the engine, changing the manifold vacuum. As the vacuum changes, it draws the piston up which causes the piston-needle to raise (allowing more gas to flow out of the main jet). Be careful not to bend the piston-needle!

Good luck!
 
OK, I am starting to figure it out. The diagphram is new, so are all the seals. It I am not getting the needed vacuum. I think the vacuum comes from the cannister, so it sounds like that could be the problem. That will give me something to check when I get home tonight. Thanks for the help, I will do some checking and post the results.
 
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