I'm running a 401 Nailhead in my 28 Model A. I have a re-occurring choke problem. The pull off piston in the choke housing gets stuck in the choke-off position. This happened when I first got the engine together and installed (stock carb, freshly overhauled). I took the choke housing apart and really couldn't find anything wrong. I used some fine sand paper on the bore and got everything operating smoothly. It worked fine for one or two starts, then the choke wouldn't close anymore because the piston was stuck in the bore. Fiddled with it some more then finally took the complete choke housing off and Edelbrock carb I had. It seemed to work okay until the other day when I went to start it and it was apparent that the choke wasn't working. Checked it today and the pull off piston was stuck again. Anyone run into this?
Those carbs originally had a heat pipe that ran air through a passage in the exhaust manifold for a heat supply to open the choke. It got fresh air from the filtered side of the air cleaner / carb air horn area to keep the system clean. It looks like you're running headers and an electric choke and not using / needing a hot air supply. Is the fitting on the choke housing (for the heat pipe) plugged, or are you getting contamination pulled through there that is causing the piston to stick?
Not to sound like a wise guy, but since you tried a completely different choke assembly and it acted the same way, is there a possibility that the problem is elsewhere? Binding choke shaft? Linkage hung up?
With the exception of a very few water heated chokes, integral choked genuine Carter carbs of the day have a "heat tube" connected that pulls hot air in to release the choke thermostat spring. On some models, the free end of the tube fit into a "stove" in the exhaust manifold; others connected to a tube pressed into the exhaust crossover of the intake manifold. The pressed-in tubes were normally good for 30~35 years before failure. Always a good idea to replace this tube when doing an engine that has one. The pull-off piston sticking in the choke housing is a classic symptom of an exhaust leak in the hot air source, allowing raw exhaust to be pulled into the choke housing. Once the exhaust leak is eliminated; one can pull the access Welsh pull on the choke housing (many are 11/16 inch, but measure first, and acquire a new one), and lightly hone the cylinder in the choke housing with 1200 grit emery cloth. Install the new Welsh plug, and you are good to go. Note that you are using an electric choke, which is obviously not original. If the electric choke were installed because the superior hot air choke was giving an issue; the housing may be damaged from before, and still need to have the cylinder honed. Jon.
Carbking , is the winner ! Exhaust gas is getting into the chock housing causing , the “ carbon “ issue . Clean it well , disconnect , the stove pipe and allow the electric housing to warm and open the choke . Seems to me this is what a newer Edlebrock “ AFB” does .
I am no expert on electric chokes. If this was a carb with an exhaust heat choke with electric added there is still a vacuum being drawn into the stove chamber. If it is plugged now I would think a small amount of air would be needed to make it properly work. I bow to carb king…
I agree that is the most likely cause, but I'm not running a choke stove. The main reason being that I'm running headers. Also, when the choke works, it works perfect. Engine starts first try, goes to high idle, and no flat spots or stumbles. I comes off at the correct rate also. The Buick has a strange carburetor base gasket with a stainless plate and some exhaust passages. However, I don't believe there is any connection to the choke assembly, but I could be wrong. When the piston sticks, it isn't stuck hard, just enough to keep the choke plate from closing. Most of the time it takes very little to un-stick it. I'm at a loss as to what could be causing this. The Edelbrock assembly I installed came of a carburetor that I ran on my truck and it never had this problem. It is something related to the Buick engine, but I don't know what.
I thought that also, but everything is free. It is the piston in the pull-off that is sticking. Most of the time it is barely stuck in that it takes very little to un-stick it.
I don't believe the Edelbrock choke assembly has a choke stove passage. The same problem occurred with both the original choke assembly and the one I have on it now.
On the original choke housing I did pull the welsh plug and clean the bore. I found a carb supplier in Washington that had the correct plugs. It didn't make any difference. The bore actually looked pretty clean for a 35 year old carburetor.
Have done thousands of Carter AFB's. Maybe 3 or 4 had the screws in the choke butterfly shaft off-center just enough that the butterfly would stick in the airhorn. Dr. Goodpliers occasionally works on AFB's. I am not a lover of electric chokes: https://www.thecarburetorshop.com/Automaticchokes.htm The hot air choke is much more user-friendly for those running automatic transmissions. Making one work with headers is quite simple; you just need to fabricate and install a heat stove. https://www.thecarburetorshop.com/Heatstovefabrication.htm Jon
As an update; I took the original housing apart again and cleaned the bore and piston thouroughly. After I cleaned things up I flooded the bore and piston with WD40. I've driven it for the last week, although not a lot of miles, and the choke piston is still free in the bore. It's the first time it hasn't locked up since I've been fooling with it. The funny thing is that I've done the same thing multiple times (except for the WD40), hopefully this time it stays free.
Actually a properly operating electric choke or automatic choke, opens the choke plate a bit as soon as the engine starts to create a vacuum. That's maybe 5 seconds or less. I have found that the electric chokes open much faster than those that used a choke stove. I like my vehicles to start quickly when cold and be able to drive away in a minute or less without stumbles. My 64 Chevy truck and 57 T-Bird do just that and both have electric chokes.
If you look at a car that came with a manual choke, the choke butterfly has a spring loaded door in it that opens the second it gets vacuum to it. This keeps the carb from flooding the engine. When you add a manual choke conversion to a carb that came with an automatic choke, it doesn't have the spring loaded door in the butterfly. Thats why the conversions work so poorly.
Back in the early 70's I worked at a Lincoln/Mercury dealer. We had a new Eliminator 1 Cougar which had a Boss 302 and a 4 speed. The Cougar had a Holley 4bbl with a manual choke. There wasn't a salesman who could start the car. Most didn't use the choke at all and stalled it multiple times. The others pulled the coke out and flooded it. At any rate it always had a dead or dying battery. If you used the choke properly it started and ran fine. It was sold to a young lady, probably about 20 years old. It must have been trouble free as I don't think she ever brought it back for any warranty work.
In a different lifetime, well, maybe close to 50 years ago; the wife had an almost H.A.M.B. friendly vehicle with automatic transmission. The heat tube in the manifold burned out, and I didn't have time to fix it right. Pulled the Welch plug in the choke housing, honed the cylinder, and put on an electric choke. This occurred in either very late fall, or early winter, memory not as good as it once was, but the temperatures were below freezing. Checked it out to be working. Left the next morning (still had a "day" job, and running the shop evenings and weekends) leaving my wife with her car. Got home that evening, and wife was not happy. Car stalled three blocks from home, and would NOT restart! She had to walk! Checked it out, no problem that I could find; and left it alone. Next day, exact same result, except she says "you get this thing tomorrow, leave me your truck", yes she can drive a stick transmission. She learned on a 327/340 in a 1963 Corvette. Had zero issues the next two days, and we had a weekend. So tried to duplicate exactly the problem. Started the car the same time she normally went to the store, and took the same route. CAR STALLED AT THE STOP SIGN 3 BLOCKS FROM THE HOUSE! Opened the hood, removed the air cleaner, and the *&^%$#@ electric choke was wide-open??? Left the air cleaner off for 15 minutes to give the choke a chance to close; restarted the car, and drove home. Did some testing. Choke took less that 1 minute to fully open. Automatic trans was not up to temperature, and would stall the engine at idle (dependent on the position of the choke) and the engine would not restart with no choke! Spent the rest of the weekend removing the manifold, fixing the heat tube, and reinstalling the hot air choke. And got my truck back! The hundreds of fragments of that particular electric choke are somewhere in a central Missouri landfill! The hot air chokes time to go off are keyed to the temperature of the engine, not to a fixed time, as are the electrics. MUCH more reliable for older automatic transmissions. And I still don't like electric chokes! Especially on H.A.M.B. friendly vehicles with automatics. Jon.
I think I've solved the choke problem. The nailhead engine has an exhaust passage cut in the manifold that warms the bottom of the carburetor. Since exhaust gas is right at the bottom of the carb, there is a stainless plate that goes between the carb and the carb base gasket. It seems someone (me) left the stainless plate out. The bottom of the carb and the choke pull off passages were full of wet exhaust soot. I've got a plate and new gasket coming. If you look at the intake the passage from one side to the other opens into the exhaust. I also tapped the holes and plugged them while I'm awaiting the new plate and gasket. I'll bet it will even idle smoother.
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