Carb Preflight Prob...
 
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Carb Preflight Problem

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Karl A. Vogelheim
Posts: 114
Estimable Member
Topic starter
 

For the last two times I have gone out to my airplane, when I turn on the fuel valve, I get fuel leaking out of the carb drain.  I am not willing to fly the airplane this way but I am trying to figure out if this is something simple like a float replacement or if I should get he carburetor overhauled?  I have tried tapping on the carb with a rubber mallet to see if the float is stuck and that has not solved the issue.  So any advice on this situation would be appreciated to include recommended carb overhaul shops.  

Karl A Vogelheim
S108-3 N596C

 
Posted : 08/06/2022 2:24 pm
Bret and Bret reacted
lawheelock
Posts: 774
Prominent Member
 

Your mistake may be in shutting off the fuel.  A proper functioning carburetor float valve will not leak.  Your float may be set too high or perhaps the shutting off the fuel allows the neoprene tip on the float valve to dry out to where it allows fuel past it when the bowl is full.

What plane, what engine, what carb?  more information is always helpful.  I think -3 with 165 engine.  MA 4-5 Carb?  There are new floats that dont absorb fuel and sink.  Your carb may have an obsolete float and float valve in it.  They can be replaced without an expensive "overhaul"

I have owned my Stinson for 54 years and almost never shut the fuel valve off and the only times I have had leakage past the float valve was when there was a curable problem. Originally my Stinson was powered by a Franklin 150.  Over the years I had two different engines on it and two different MA-3 carburetors.  In 2012 I installed an O-360 180 hp with MA 4-5 Carburetor.  I leave the fuel valve on.

Larry Wheelock, A&P/IA

Larry Wheelock, A&P/IAStinson 108 N584LW 180 LycTexas in Winter; Indiana in Summer

 
Posted : 06/07/2022 5:27 pm
Karl A. Vogelheim
Posts: 114
Estimable Member
Topic starter
 

I should come on here more often as I have resolved this issue. Not being sure what was going on, my mechanic and I decided to try the simple things first, we pulled the drain plug on the carb (I suppose this is the carb float bowl drain plug to be more accurate) to see if there was any debris in the carburetor. Nothing was found. We put the plug back in and turned on the fuel. No leaking. We let it sit for a while and turned the fuel back on. No leaking. We started the engine and ran it for a bit and then shut it down. No leaking. In fact it hasn’t leaked since we checked this out. I can’t explain it but it has been perfectly normal since this inspection. I am happy as I run well and it didn’t really cost me any money. 

To be more specific I have a 108-3 with a Franklin 6A4-164-B4. I am pretty sure that has the Marvel-Schleber MA4-5 for the carburetor. In any case, this isn’t a problem any more.

Karl A Vogelheim
S108-3 N596C

 
Posted : 17/10/2022 4:03 am
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