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Unknown Carburetor fitting

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.
 
Yes, that's for the carb temp sensor, and it is 1/4-28 threads. Not sure why a pipe fitting would be there.

Vic
 
alpinelakespilot2000 said:
I think that's where my carb temp probe goes. Not sure what a fitting would be doing there!
Click to expand...

I thought the carb temp fitting was the plugged fitting higher up in this picture (above the data plate)? In every single picture I can find of the MA4SPA, the location shown with the fitting here is another plugged hole. An alternate location for the probe maybe? But certainly doesn't explain what an AN fitting would be doing there.

A carb temp install manual seems to show the same https://www.aircraftspruce.com/catalog/pdf/icemaninstall.pdf

In researching this I stumbled across a manual with the best diagrams I have seen of an MA4SPA. http://www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf

Chris
 
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Not the carb temp 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...
 
snopercod said:
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.
Click to expand...

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.
 
It looks like that hole shouldn't even be threaded. Pic straight from MSA Carbs -

10-3678-32_29.jpg


The threaded plug in the carb temp location can clearly be seen higher up.
 
Auto fuel?

G-force said:
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.
Click to expand...

Some attempt perhaps at keeping liquid fuel circulating and returned to the tank to prevent vapor lock using auto fuel?
 
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.

Couldn't tell any difference in the idle or full power performance of the plane after plugging the hole.

Sorry, but I'm 10,000 miles away from my plane, so can't provide any part no's.

Is is a casting hole?
 
PCHunt said:
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?
Click to expand...

When I went to install the carb I looked through the barrel to see what I could see. It appeared as though the hole went through the casting and into the open barrel. At the time I didn't think anything about it because I KNEW the plans would show me exactly what it was and how it connects.

Next time I'm at the hangar I will look at it again, maybe this afternoon, and take some pictures of the inside of the barrel. Too darn cold to go this am - 20 degrees. Brrrbrrrbrrr!
 
That hole doesn't go into the float chamber. If memory serves it goes directly into the carb throat before the throttle plate. Can't guess what the previous owner was using it for. Was the fitting restricted and being used to deliver primmer fuel? Maybe trying to measure ram air? Only the Phantom knows for sure:)
Good Luck,
Mahlon
 
snopercod said:
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...
Click to expand...

You are correct. The temp probe hole is higher. I see it now.

Vic
 
No history, got it from Ebay with the disclaimer "you are responsible for checking compatibility and airworthiness, etc."

Here's a pic of the inside of the barrel showing the inlet side of that fitting.

 
Manifold Pressure?

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:

DkQE3C.jpg
 
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snopercod said:
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:

DkQE3C.jpg
Click to expand...

Manifold pressure would need to be taken after the throttle butterfly valve.
Good Luck,
Mahlon
 
Well duh...

mahlon_r said:
Manifold pressure would need to be taken after the throttle butterfly valve.
Click to expand...
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?
 
snopercod said:
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:

DkQE3C.jpg
Click to expand...

Pitot tube for the Venturi
 
Vent

Guessing it was a connection for a crankcase vent!
Similar to an automobile engine.

Think how Anti-Splat uses the exhaust for suction...
The carb may pull a similar suction.

Just guessing
 
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