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Need info and gasket for a stromburg.

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S

scoobiedoo

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I have a 75 Midget that appears to have a spit engine in it (points ignition, different "Temperature compensator" mechanical choke)

I bought a rebuild kit for a Midget and it dosen't have the proper gasket for the mechianical choke unit. I was wondering if anyone knew of a source for this single gasket.

Also the "temperature Compensator" and "bypass valve", what ate their functions? I assume they are part of the idle air control system but am a bit foggy. My temp comp plastic valve peice is pitted and cant fully seat and seal, is this a serious problem? And finally my bypass valve appears to have been sloders in such a way as to make it stay closed, would this cause it to not idle?
 
SD. There is a paper thin gasket between the choke module and the carb body, but I have rebuilt carbs without using it. If you clean the mating surfaces and carefully apply something like Hylomar or another gas resitant sealant, you'll be OK. Be careful and don't gob it on because if any gets on the disc with the fuel ports, the choke will be difficult to operate.

The temperature compensator: think of it as a "mini choke". When the carb temperature is less than 100* it closes a 1/4" port on the carb's air box (air filter housing) mounting flange. As the temperature rises, the bimetal strip thermostat opens this port fairly quickly to allow fresh air thru the 1/4" hole into the carbs mixing chamber.The temperature at which the bimetal strip opens the pathway is adjustable, but not critical, it's affect in the big picture is not very much
The plastic cover is not designed to be air tight and frequenly seen slightly warped from exposure to under bonnet heat.

The Throttle Bypass Valve: It is designed to open when it senses a high vacuum in the intake manifold during engine over run, sudden deceleration.
If it does NOT OPEN under those conditions you MAY hear a popping in the exhaust as you downshift gears.
If it does NOT CLOSE after you come down from speed to an idle, the idle speed may hang up because of an excess of fuel bypassing the throttle disc. A qiuck blip of the accelerator will probably suck the valve closed and the idle return to normal.
If someone somehow has disabled it, it's probably in the closed position and you may hear popping rather than the familar gargling sound in the exhaust during a downshift.
Seems like a lot of people disable the TBV instead of either replacing the valve/ diaphram component when it tears or becomes brittle or don't make the spring tension adjustment on the valve.

Neither of those components in themselves would cause the engine not to idle.
If it's not able to idle, it must be something else.
 
Thanks for the help, the port that leads to the Temp Comp and the Idle Mixture screw was clogged by mud daubers. I assume if the idle mixture screw isnt getting any air it might not idle? Only other thing I can think of is either improper float level, as it seems to idle for a bit than start to stall and then if you blip the throttle to keep it running it will idle a bit more, or a vaccume leak.

Also, my carb dosent seem to have a vaccume port for the distributer, would a port of the manifold be ok?
 
The idle trim screw ? Well. it really doesn't change the mixture all that much. In fact the manual says that the only real way to detect any change it might make is with an Oxygen sensor at the tail pipe. Also it is suggested to fully close the idle trim screw, shutting off that bit of air once the engine has "broken in".
The real mixture adjustment is done by raising and lowering the metering needle, if your's is the type of ZS that has an adjustable needle. If the needle is not adjustable, it might have an adjustable jet like the SU carbs, but if it has neither then the only other way would be by adjusting the height of the floats.
Hard to say where the vacuum port, if any, might be on that carb. The usual place is on the bottom of the carb, just outboard of the carb to manifold mounting flange, just about where you'd imagine the throttle disc to be.
Check for freedom of movement of the air valve and also the condition of the rubber diaphram that surrounds the air valve.
One component that is often troublesome in a carb that has not been used in a while is the float chamber's needle valve.
Sometimes it sticks in an open position, flooding the carb; sometimes in a closed position, starving the carb or anywhere inbetween open and closed.
Let us know how you make out; if it continues to act up we can come up with some more possibilities, like a clogged fuel filter, faulty fuel pump, etc, etc.
 
Thanks for the help, the fact that it runs fine off idle and revs fine tells me that the pump should be fine, and the filter should be ok too but ill cheak that. I found another ZS that is from an MG midget and am gonna buy a rebuild kit that appears to have gaskets for both water and manual choke so that should solve my choke gasket issue.

As to the needle valve it appears to have been replaced at some point with a "Grose" type valve and it seems free enough.

For damper oil in the dashpot would 30W silicone R/C shock oil work, or is that too thick?
 
That's a good choice of oil as far as viscosity. I'm not sure that silicon does so good on rubber such as the diaphram should it overflow the damper. I just don't know.
The only problem I've had or heard of with the Grose jet is that they may fail to shut off the gas supply.
I guess it would be a good time to repeat the old saying. "90% of carb problems are ignition problems".... Just in case.
 
I had trouble with the grosse jets. Kept flooding out. Once I broke down, and disabled the fuel pump(MGB electric), and spun the car over, wide open throttle, to get the gas out. When it finally died, I reconnected the pump, spun the motor till it cranked, and hauled a--, to keep it running.
I replaced everything, including the floats, and installed a pressure regulator.
I think the grosse jets may be okay, if you use a pressure regulator.
Emmett
 
That's pretty good, Brooks. I just love it when somebody outsmarts one of these old cars.
 
Thanks for the help, silicone is generally a good idea for rubber as it will keep the rubber pliable and not dissolve it. Do you tghink the jets would cause the stalling after a short idle issue i have? I have a Weber DGV that i am rebuilding and the mainfold for it, do you think its worth my time to swap, i know the ZS is not the best carb design ever.

One more question, what do you think I can get for a rebuilt ZS? not shiny new but it spent time in a cleaning tank so its not too bad.
 
SD, the ZS jets don't usually present a problem. The metering needle goes right thru it and keeps it clean.
I'd suggest checking the going price for ZS's on eBay Motors.
I think that the Weber might be a little more difficult to get set up, but once you have the metering correct, it should do alright. I don't think it will transform the engine into a powerhouse, though.
 
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