Fuel System: Stromberg EX-23: Sticky choke valve

[southbend]

Stromberg EX-23 on '35 Dictator 2A. The choke valve doesn't always close completely. It seems to sometimes get hung up maybe an 1/8" from full close and I have to poke it with my finger to close it. When I do that I feel like there is something binding. Once done, the car starts fine. Shut it off and sometimes it restarts, sometimes not. I read through the shop manual but can't really find anything that addresses this problem--just adjustments, etc.--but I'm not sure what I need to adjust. I'm no mechanic so I thought before I tear into it and do more harm than good, I'd go to the experts.

What say you?

This is a photo of the valve in the stuck-slightly-open position.

Thanks again for sharing your expertise.

Mark

[skyway]

Not familiar with this particular carb, but is that the choke stove, or some sort of bi-metalic choke control spring on the manifold in the upper left corner of the pic? If its not a simple adjustment to tighten the spring assembly, I would think you are looking for binding or slop in the choke linkages, corrosion or an obstruction in what ever that heating device is, or perhaps even wear in the choke flap shaft, or where that shaft goes thru the carb housing. The slightly later carbs (like the BXOV on my 1941 Commander) with the choke housing mounted on the side of the carb, had a stove tube that went thru the exhaust manifold, was open on the bottom, and used vacuum to draw heated outside air into the choke housing. If exhaust gas rusted out that tube inside the exhaust manifold, exhaust gas would get sucked into the choke housing and cause that to corrode or get gunked up on the inside? Hope this helps?

[garyash]

The choke stove is built into the lower cast-iron section of the EX-23 carb. There is a coiled spring of strip steel inside the rectangular box. The spring controls the closed position when cold and opens the choke when hot. It may help to take the cover off and clean the parts. Note the alignment of the arms on the outside and the pin on the inside when you take it apart. You'll neeed to make a new thin gasket.

[skyway]

Interesting!
So what is that I see on the manifold in the upper left corner of Mark's photo?
Not being critical, just curious?

[garyash]

Yes, Skyway, that is interesting and curious! I just checked the Master Chassis Parts catalog for 1928-40 and a 1937 Shop Manual (don't have 1935). Indeed, there is a thermostat assembly on the manifold, as well as the one on the carb. Studebaker and Stromberg, in their infinite wisdom, had different versions of the EX-23 in 1935, 1936, and 1937, but they all seem to operate the same basic way. My 1937 Shop Manual has 5 pages on the operation and adjustment of the choke system. The thermostat on the carb itself is augmented by a small vacuum-operated piston and is used to control the choke shaft for the three idle speed cam positions on the main throttle shaft and to partially open the choke once the engine is started. The thermostat on the manifold seems to force the choke open when the engine is finally warm. Both mechanisms are solidly connected to the choke shaft with small rods. Maybe they take a vote on which way to push the choke shaft. Certainly, the adjustment procedure on 78-year old carbs and thermostats will be fiddly.

Since I have a large pile of EX-23 carbs that I bought in my search for four good, complete ones, I looked at the differences between the carb versions. The 1935 carb has a 1-3/32" venturi, 1936-7 are 1-5/32". Stromberg also added a thick insulator between the cast iron body and the upper zinc part in 1936, which forced changes in the rod lengths, etc. There seem to be a different pump piston and other small parts each year. I can only assume that the 1937 versions are supposed to work better than the early ones.

[skyway]

Thanks Gary. Always something new to learn on these old cars of ours!
I wonder if this manifold control is also subject to inhaling exhaust gas if a baffle or something leaks or corrodes?

[skyway]

OK, here we go! My 1946 MOTORS manual provides adjustment info for both the EX-23 carb, and it's manifold thermostat. Too much for me to type in on this smart phone, but I can photocopy and mail if needed. In the alternative, because 1935 is the earliest year covered in my 1946'edition, you should be able to find this info in a 1946 or earlier MOTORS manual. Lemme know.