The Murphy Builders Site

First off all, I am not a mechanic..

Are the tanks valves open when engine is sitting not running? If not, it
explained why it was not leaking... Could a leaking intake cylinder valve
"push" some "air" back in the carburator...? May be that question is the
proof I am not a mechanic! lol

Jean Poirier
Pr

Things to check:

What is the pressure being supplied to the carb? Perhaps too high?

Check the float for correct height.

Check for cracks in the casting, or perhaps a pinhole somewhere.

.." it only leaks when it is running" ...
Does this mean at idle, or at some higher RPM?

Do you see the leak continually? or does it abate after it has been idling
for a bit?

If it only leaks when it is running, I would suspect that the fuel pressure
is too high.

Tim Hickey.
R808


----- Original Message -----
From: <indabush@hay.net>
To: "Rebel Digest, " <rebel-builders-d@dcsol.com>
Sent: Tuesday, October 14, 2008 2:26 PM
Subject: [rebel-builders] Marvel Schebler / Facet Carburetor

Has anybody ever had ..................... ?

I have a MA-4SPA carb that has a persistent gas leak - small amounts of
fuel come down the throat and drip out the air box. It doesn't leak just
sitting there, only when the engine is running. The carburetor has been
removed and inspected twice. The seals and gaskets, needle and seat, and
float are new. There was blue dye around the discharge nozzle, and the
nozzle was removed and inspected and new seals installed. The engine runs
normally and is not too rich. Could a leaky primer cause this?

Any suggestions?

Mike, C-FNBO





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If the float level is set to high it will leak from the normal discharge
nozzle. The specifications are probably in the carb oh manual specified
for the part number such as --- Lycoming # 10-xxxx. Does it run rich
and need to be leaned out to idle? At about 1000 RPM you should be able
to lean 25 - 50 rpm before the engine starts to die. If you have closer
to 100 rpm then it is too rich.

Dick Wampach SR-108

Marvel Schebler / Facet Carburetor

Has anybody ever had ..................... ?

I have a MA-4SPA carb that has a persistent gas leak - small amounts of
fuel come down the throat and drip out the air box. It doesn't leak just

sitting there, only when the engine is running. The carburetor has been
removed and inspected twice. The seals and gaskets, needle and seat, and

float are new. There was blue dye around the discharge nozzle, and the
nozzle was removed and inspected and new seals installed. The engine
runs
normally and is not too rich. Could a leaky primer cause this?

Any suggestions?

Mike, C-FNBO





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At 03:26 PM 10/14/2008 -0400, you wrote:

Has anybody ever had ..................... ?

I have a MA-4SPA carb that has a persistent gas leak - small amounts of
fuel come down the throat and drip out the air box. It doesn't leak just
sitting there, only when the engine is running. The carburetor has been
removed and inspected twice. The seals and gaskets, needle and seat, and
float are new. There was blue dye around the discharge nozzle, and the
nozzle was removed and inspected and new seals installed. The engine runs
normally and is not too rich. Could a leaky primer cause this?

Any suggestions?

Mike, C-FNBO

Hi Mike I don't think gas could get back down the intake tubes from a leaky
primer but has anyone checked the accelerator pump? Have you figured out
yet if it's leaking at all power settings or just at idle? If the idle
speed is too low there might not be enough vacume to draw all the fuel in.
Drew



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Jean, Tim and Dick: Thanks for input on the carb gas drip problem.

Here is the answer to your questions:
I usually turn of the fuel when sitting, but I have left it on and there
are no drips.
Fuel is gravity feed, so the pressure is just the head from the wing tank.
Float level has been correctly set.
No evidence of cracks or leaks from the casing.
I'm not sure whether it is dripping at idle or at power. Not sure how to
check that out.
The engine may be running a little rich. When the plugs were inspected
they were not fouled, but more black than brown in colour. On the other
hand, very little leaning is required to reach peak rpm at cruise, and I
only get about 25 rpm or a little better. I will check it at idle.

The AME recommendation is to send the carb away to a specialty shop.

Mike Ash, C-FNBO






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One thing I get with FOKM is if I turn the fuel off and let the carb dry
out, when I turn it on again a few days later, the carb leaks like a
sieve. I let a little fuel get into the carb and soak the seals, the
seals swell up and 15 minutes later it no longer drips. Needless to say,
I don't generally turn the fuel off except when the plane is going to
sit a long time.

Garry

indabush@hay.net wrote:

Jean, Tim and Dick: Thanks for input on the carb gas drip problem.

Here is the answer to your questions:
I usually turn of the fuel when sitting, but I have left it on and there
are no drips.
Fuel is gravity feed, so the pressure is just the head from the wing tank.
Float level has been correctly set.
No evidence of cracks or leaks from the casing.
I'm not sure whether it is dripping at idle or at power. Not sure how to
check that out.
The engine may be running a little rich. When the plugs were inspected
they were not fouled, but more black than brown in colour. On the other
hand, very little leaning is required to reach peak rpm at cruise, and I
only get about 25 rpm or a little better. I will check it at idle.

The AME recommendation is to send the carb away to a specialty shop.

Mike Ash, C-FNBO






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