I think that's where my carb temp probe goes. Not sure what a fitting would be doing there!
No idea but the fitting appears to be at about the fuel level in the bowl. My carb has a plug in the casting right there.
Wild speculation and ramblilngs on my part, I know nothing abut airplane carbs: If it is installed right the the fuel level in the bowl, it may be some sort of overflow. It is pretty common on off road vehicles with carburators to install such a system. The extreme shaking up and down lifts the float up and down, overfilling the float bowl causing stumbling. Some systems go as far as using an auxiliary electric pump to continuously draw off the excess fuel from a fitting placed in the bowl at the desired fuel level.
During an annually-performed condition inspection, I recently discovered that this hole on my carb was open. I purchased a small lead ball that is made specifically for the purpose of plugging the hole. Very easy to install, just "peened" the ball gently.
Is is a casting hole?
Yes, the carb temp hole is at the top, just below the mounting flange. I know this because that plug fell out of my carb and I flew with it that way for months. It didn't seem to make a lot of difference. Go figure...
Manifold pressure tap?
Originally I would have sworn that fitting penetrated the bowl, but I see now that that's not the case. The bowl is C-shaped and that fitting goes into the barrel as your latest photo showed:
Well duh...You're right, of course (slapping forehead). OK, how about this? My 1" mechanical fuel pressure gauge is a differential pressure gauge. The high side is connected to the inlet of the carburetor and the low side is connected to the airbox. Could that be what the mystery fitting is for?Manifold pressure would need to be taken after the throttle butterfly valve.
Manifold pressure tap?
Originally I would have sworn that fitting penetrated the bowl, but I see now that that's not the case. The bowl is C-shaped and that fitting goes into the barrel as your latest photo showed: