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Extremely Rich at cold start


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1941 Special series 40.

 

I cleaned the carb with sea foam treatment using the aerosol upper engine cleaner hose in the carb and the bottle in the gas tank. I ran the gas tank empty after 115 miles (15.5 gal, yikes but I did do a lot of idling as this was the first drive of the year).  refilled the tank with 91 non ethanol as usual. This treatment really helped smooth out the tip in throttle and responsiveness however now every time I start the car from a cold start my concrete is black full of soot and water/gas condensate on the floor. The car surges for the first 2mins until then it’s smooth as can be. This black soot and rich condition only happens when the engine is started cold. I never remembered this happening before. I would definitely noticed it before because if I back the car in my garage wall and first row of cinder block turns black!

Thoughts? 

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Could it be that you cleaned the choke plate and the spring which actuates it so well that it is absolutely closed, and just takes a bit till it opens?

Try turning the round plastic (bakelite) control to be a bit more on the "LEAN" adjustment

There are screws holding it in adjustment so you can loosen it a bit, turn the cap, and tighten again  - trial and error - you want the choke to close almost all the way when cold and you kick the gas pedal, but start to open as heat relieves the controlling bi-metallic spring which is wound inside the case

 

Good luck

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9 hours ago, Marty Roth said:

Could it be that you cleaned the choke plate and the spring which actuates it so well that it is absolutely closed, and just takes a bit till it opens?

Try turning the round plastic (bakelite) control to be a bit more on the "LEAN" adjustment

There are screws holding it in adjustment so you can loosen it a bit, turn the cap, and tighten again  - trial and error - you want the choke to close almost all the way when cold and you kick the gas pedal, but start to open as heat relieves the controlling bi-metallic spring which is wound inside the case

 

Good luck

I will give this a try. I read the service manual and didn’t realize this is adjustable. 

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No matter what I do, my Limited spits a bit of black water when I first start it. I accept it as normal. I've done a LOT of tweaking to the carburetors and it starts instantly and idles smoothly even when cold, so I think I have things finally set up right. But the black soot is unavoidable. Remember that water is a by-product of combustion and when you first start, the exhaust system is going to be cold, which causes the water to condense on the walls of the exhaust system. When you rev it, the water gets spit out, taking the soot with it. Once it warms up, the water stays as vapor and this stops. I think it's totally normal and isn't limited to just our Buicks. All old cars do it to some degree.

 

Play with the choke a little bit and see if idle quality improves when it's cold. I found that I needed far less choke than I thought, especially since we only drive the cars when it's relatively warm out. Mine was actually flooding in the cold so I knew the choke setting was too rich. Dial it back and see what happens. At worst, you run without any choke action at all when you start but it won't affect how it drives once it's warmed up.

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Idling, if the idle mixture screws are set via vacuum gauge, will be overly rich (even though the engine seems to idle nicely), and will deposit some black soot in the tailpipe.

 

When the car is started, as Matt stated, there will be water condensation in the exhaust, which is heavier than the normal warm exhaust, and will sweep the previously deposited soot out the end of the tailpipe.

 

The while tailpipe, universally accepted as the mark of a well-tuned engine of yesteryear......................................was lead residue.

 

But the automatic choke assembly is adjustable: Automatic chokes

 

Jon.

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I spent the day trying to adjust the choke. I was able to reduce the choke to just barely grabbing above the throttle notch. It was 42deg out all day so that works. I am not sure if the carbon was reduced any on startup. I am starting to think that as stated above it’s the condensation Continuing to wash out the exhaust pipe from when I cleaned the carb. That was a black smoke 💨 for 10mins from the cleaner. 

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