carburetor overhaul

FORANE

FORANE

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FORANE
I cancelled a flight today after finding fuel leaking from the rear of the carburetor on my O-320. It appears to be coming from the o - ring where the mixture arm engages the carburetor.

The local A&P said he may be able to simply replace the o - ring and fix the leak.

What is the recommended TBO on carburetors? Would I be well advised to just overhaul it now?
 
Normally a carb is good for the life of the engine. O-rings can get hard with age and leak. If it can be replaced by your AP drive on.
 
That mixture arm is part of the top plate of the carb, if your fuel level is that high, there are other things that should be done first.
1 find out why the fuel level is that high. most likely the inlet float valve is leaking, allowing the fuel to rise to a point it can find to get out of the carb.
2 floats are sticking, and not shutting off the fuel when the proper fuel level is reached.
both of these discrepancies are easy fixed.
I wouldn't replace the carb with out knowing why I was changing it.
might be as simple as a piece of dirt in the inlet valve.
 
your MA3-SPA doesn't have a o-ring on the mixture control shaft.
 

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Your A&P will remove your carb to partially disassemble and troubleshoot it (hopefully). Last summer I had an intermittent fuel leak from my O-320 carb. I also had recently noticed that I was no longer getting a sharp engine cutoff after pulling the mixture. A&P took the carb apart and recommended a new inlet valve, as Tom mentioned. I also had a metal float which (I think I remember...) had an AD for inspection and/or replacement due to possible leaking causing the float to sink, risking complete engine failure. I decided to replace the float also, with a new, blue, composite float. A&P said that everything else inside looked good. I have had zero issues since.
 
Thanks for the replies. We haven't removed the carb yet but the A&P did mention a possible needle valve issue (I think that's what he called it).
 
Yep. Needle valve. That was what I replaced, along with the float assembly. Aircraft Spruce had the parts. Weren't horribly expensive - I believe around $300 for the needle valve, float and assorted gaskets. Worst thing was the freight. I was in a hurry to get back in the air, so I overnighted the package from California to Colorado. $90. :)
 
I had an old copper float still working after half a century. A&P advised that the matching needle is no longer available. so he's ordered a new needle and plastic float.20190411_125629.jpg
 
FORANE said:
I had an old copper float still working after half a century. A&P advised that the matching needle is no longer available. so he's ordered a new needle and plastic float.View attachment 73317
Click to expand...
Your carb will no longer be auto fuel compliant.
What is wrong with the inlet needle valve? Is it a rubber tip or steel?
OBTW the new needle can be bought.
 
FORANE said:
I had an old copper float still working after half a century. A&P advised that the matching needle is no longer available. so he's ordered a new needle and plastic float
Click to expand...
If you are going to throw the brass float away throw it my way. I use them to build auto fuel carbs
 
Tom-D said:
Your carb will no longer be auto fuel compliant.
What is wrong with the inlet needle valve? Is it a rubber tip or steel?
OBTW the new needle can be bought.
Click to expand...
Looks rubber to me. No idea what is wrong other than the A&P said it was leaking and needs to be replaced but wasn't available.
I have 10:1 pistons and composite fuel tanks so no auto fuel for me anyway. ..
20190411_125139.jpg
 
FORANE said:
Looks rubber to me. No idea what is wrong other than the A&P said it was leaking and needs to be replaced but wasn't available.
I have 10:1 pistons and composite fuel tanks so no auto fuel for me anyway. ..
View attachment 73320
Click to expand...
As shown, that is the latest version needle.
and
There is nothing wrong with your float either.
 
If it doesn't slosh when you shake it, the float is fine. The delrin tipped needle will last a good long time. It could simply be out of adjustment.
 
Tom-D said:
As shown, that is the latest version needle.
and
There is nothing wrong with your float either.
Click to expand...
Tom, doesn't Marvel-Schebler say to stop using the metal floats in their carbs and go with the poly something, something, not plastic, just seems like I read something about that in the M-S manual
 
Gary Austin said:
Tom, doesn't Marvel-Schebler say to stop using the metal floats in their carbs and go with the poly something, something, not plastic, just seems like I read something about that in the M-S manual
Click to expand...
Yes,, they like to sell parts.
 
Overhaul completed, reused the copper float.
thanks guys
 
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