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My 1954 3100 235 has not been tuned up in a while. It has always ran great. It is now cold and I started it up to warm up before I left the house. As usual, I had to have full choke until the engine slightly warmed up and then I only back off the choke a little bit. Recently I noticed it seemed to be running just a little bit rough. It was hard to hear a distinct miss fire. I later noticed the exhaust left a residue on the driveway. Very heavy carbon build up. It was much darker than the pictures really shows. Two different days. It looks lighter in the picture for some reason.

For the engine experts, does the heavy carbon exhaust tell you anything about the engine performance and what I might need to change/fix? Simple tune-up? Timing? ?????

When was the last time you adjusted the carburetor (and, timing).

What techniques did you use?

Surprised you need that much choke, looks like I unburned fuel?

Ed

Don't warm it up, drive it.

I have had it for 3 years. It was running great when I got it and I have not touched the timing, plugs, points, condenser or carburetor other than to adjust the idol speed screw. I have always had to pull full choke to start it until it ran for a minute or two but it has always ran like a champ. it still does when I drive it. It was just when it was sitting there warming up this past weekend I noticed the exhaust marks on the driveway and it was running a little off. When I drove it there was not issue. It was running fine.

When they sit for an extended time condensation builds up in the exhaust system. When you start it it will blow it out as black or dark gray liquid. This happens especially if you only do short drives not allowing the engine to come to full operating temperature. Drive it like you stole it and put it away at full operating temp.🛠

Sounds like you are using too much choke. The plugs are probably carboned up. You probably have diluted the oil also.
George

If you have a Rochester carburetor and if you're using gas laced with ethanol and if you're not driving it very often, it is very likely your power piston is stuck in the "down" position. If this is the case, you'll be running much richer than you should. The ethanol when mixed with unleaded gas dries leaving a sticky gummy varnish-like residue which will stick that power piston as tight as if you epoxied it in there. And because of the spring, it will always be in the down position, opening the power valve fully. Good luck.

I will have to look under the hood to confirm what my carburetor is. Any chance running fuel cleaner through a tank of gas or spraying carb cleaner will clean out the carburetor? If not is my next/only option to rebuild the carburetor assuming the power piston is sticking.

There's virtually no way to do a "carburetor rebuild in a can" successfully. I agree with the idea that you've got a stuck power piston, but once the engine fires the first time and runs for a minute or so, there shouldn't be a need for much, if any choke. It sounds like it's time to dismantle and thoroughly clean the carburetor, rebuild it, and then DRIVE it more often. Short trips and "warm-up" runs are death on carburetors. Make 'em earn their keep with some highway-speed trips frequently.
Jerry

Thanks everyone for your feedback.

Given that you have done next to nothing to the engine for 3 years, think about this.
Before you dig into the carburetor:
-Check to see if the flapper valve in the manifold is free and that the bi-metallic spring is in place and in good working order.
-When you start it when the engine is cold, pull the choke out where you normally do, and pull the throttle out a bit to provide for RPM above idle (650-700ish). Once the engine starts, slowly push the choke in with the goal of pushing it all of the way is within less than thirty seconds. The above mentioned throttle knob position should provide for enough gas to keep the engine running well.
Doing these things may solve your problem without having to dig into a perfectly functioning carburetor.
How does it run once it it warmed up?
Does it leave black marks on the pavement once it is thoroughly warmed up by driving it around for a while?
Carl

It runs great once it is warmed up. Two contributing factors. The flapper valve in the manifold is stuck and the throttle cable doesn't work. I will see about getting them functional before doing anything ekse.

On my perfectly running C30 with a 292....I use Startron with every fill-up of non ethanol gas...... From my weed whacker, to my one ton....everything gets a Startron cocktail.....

You are now on Easy Street!
Fix that throttle cable and you will be able to warm up your engine with the throttle cable out a smidgen and the choke knob all the way in as described in the Operator's Manual. No more over-rich condition.
Since it runs fine once warmed up, I'll bet the flapper valve is stuck in the closed position. That is a livable situation for now.

Carl
Eh hm, "Its never the carburetor."