B100 Lower assembled and bucket test:

[Old Vintage Merc]

After finding the lost clevis pin and properly attaching the pin to the shift rod it was time to see how the motor ran.
The good news:
Engine starts great, no effort.
Green Oil Pressure Light comes on, flickers at very low idle.
Impeller working, good water flow.
Fuel pump working.
Thermostat working, water became lukewarm after running 10 minutes.
The head scratcher:
Engine idles nicely with the choke almost all the way out.
Pushing the choke IN causes the RPM's to greatly accelerate, we are talking run away acceleration.
I ran 1/2 bottle of Seafoam in 1 gallon of non ethanol 91 octane, only ran it for 10 minutes, didn't use much fuel. Hit the Stop button, soaking now.
The exhaust in the water developed a carbon slick, though barely any smoke even while running the Seafoam.
The motor hadn't been run in years, just sitting in an 86 year old mans garage.
At the very least the carburetor needs cleaning and idle adjustment.
It's going to snow tomorrow so the Seafoam will soak in the carburetor for a few days. Overall I'm very pleased with the results so far.

 

[jgmo]

Hi,
It's likely that all the setting has caused the throttle plate to stick in an open position and is allowing the engine to speed up.

Closing the choke is probably making the mixture so rich and stifling air flow so the engine is actually trying to die out but the stuck throttle plate allows it to stay running at a lower rpm.

You're right, the carb needs to be removed and cleaned.
Good luck.