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By thegasguy
#1817094
I've just had my permit inspection, with its associated maintenance work; so, to inspect for any fuel or oil leaks after the necessary removal and replacement of components, I did a quick run-up with the cowling off.
All good, with a nice improvement in tickover smoothness with a brand new set of plugs in.

I climbed out, had a look round the engine and then started to push back into the hangar.
Then- fuel started dripping from the open tubular part of the air intake system (C90- Bracket air filter) that is the lowest part under the carb.

It started well after shutdown - 3 or 4 min? - and stopped after maybe 60 seconds, all after movement over a grass surface.
The total expelled was, maybe, a decent eggcup-ful or two.

Any ideas as to whether this is normal or a problem developing?

I assume that the feed system to the carb bowl remained pressurised after the engine stopped, and for some reason the fuel "expanded" ? and overflowed out of the main jet; or else the float needle let by after the carb was jiggled about ( I don't like this scenario much)

This may well happen in normal circumstances, but I wouldn't easily see it as the fuel would run down the lower cowling to a point under the aircraft that is low and quite far back.

Anyone else seen this phenomenon ?
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By Dodo
FLYER Club Member  FLYER Club Member
#1817186
Had you been exercising the throttle after shutdown?
Although my a/c has an aftermarket electric fuel primer, the original priming system that chucks more fuel through when exercising the throttle still works and drips out the bottom of the carb.
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By Flying_john
FLYER Club Member  FLYER Club Member
#1817245
Do you stop engine with pulling mixture or from switching mags off ? (cant remember)

If with Ig switch, then I think this might point to a failing or failed fuel inlet valve controlled by the float in the carb, i.e the still pressurised fuel leaks past the valve and has nowhere to go except to squirt out the jet into the carb venturi and drip/run to the lowest point.
By thegasguy
#1817299
No movement of the throttle after shut down - I don't have an accelerator pump, so it wouldn't do anything anyway.
I have to shut down by turning the key off, as the mixture control is not designed to cause a lean cut -off on that particular carb.
Not the most sophisticated engine , but it gets me into the air !

I agree that let-by on the float valve seems likely; I'm slightly puzzled as to why it suddenly started after a few minutes of jiggling about.

It could have been doing this for years for all I know ; why it should suddenly start now I don't know.
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By rf3flyer
#1817309
I don't have an accelerator pump, nor do I have a mixture control nor indeed a key and I have very occasionally seen this when the shuttle inside my fuel shut off valve hasn't quite seated nicely. Shutting down for any length of time now, anything over an hour, I close the fuel valve with the engine running and let the float bowl run dry. Only then do I switch off the magneto and close the throttle.

I adopted this method initially as a safety measure against someone turning my prop with fuel in the bowl and a 'hot' magneto back when my 'P' lead was not in great condition. It's not absolutely foolproof (against fuel drip) but it's pretty reliable and I do do a magneto dead cut check while the engine is still running.
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By Rob L
#1817340
thegasguy wrote:... or else the float needle let by after the carb was jiggled about ...


What do you mean by "let by"?

What carb type is it? (MS or Stromberg?...if the latter, what needle type if known?)
What fuel do you use?
Nosewheel or tailwheel?
Where is the feeder fuel tank in relation to the carb?
By thegasguy
#1817561
Rob L;
Thanks for asking for info;
It's a Jodel D117, so it has two tanks.
Both feed via a valve to a gascolator - marginally above the carburettor bowl- then to a mechanical fuel pump on the front of the engine which is 'up' from the gascolator and from there to the carb, which is 'down' from the pump.
The carb is a Stromberg.
The front tank will gravity feed ( I'm told) as it's above the engine and must be used for take off and landings; the rear is probably only just about level with the carb in cruise condition.
During the event, I was using the rear tank as the front ran dry almost instantly I started the test, I caught the engine just as it started to sputter by switching to the rear tank.
I don't know the float needle valve type: the only evidence I have is that it's worked just fine on Avgas and Mogas for years and the previous owner did whatever is needed for the Mogas 'conversion' a long time back.
I've never had the slightest trouble with the fuel system feeding or leaking ( before) or the engine running rich.

In 4 years of ownership I've rarely turned off the fuel and it's always still there when I come back, and she starts straight up hot, cold and after a layoff.

I don't turn the prop without good reason, I'm well aware she will chop me up given half a chance.
I'll be doing ground runs and inspecting etc before committing to the permit test flight.

Am I even allowed to do this test flight if I make sure I'm totally isolated at the strip ?- Covid wise?
Does this count as 'necessary'? Probably not.

Anyway, I'll put some juice in both tanks and trundle about a bit as soon as I legally can, then jump out and have a look.
Report to follow.
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By Rob L
#1817627
Thanks for your detailed response.

I overhaul Strombergs quite often, and it's very rare that they don't leak (dribble) from the needle. Your problem could be a new pinhole in the brass float, which allows a small amount of fuel inside the float, hence upsetting the needle level (it could be other things too! * ).

Neoprene needles are generally considered a no-no, now. Delrin needles can also suffer from high aromatics in the Mogas. Do the documents you have describe which needle is fitted? (this should have been verified back when the previous owner did the Mogas "conversion".)
Do also bear in mind that up to 5% ethanol is not required to be declared; many other Mogas fuels contain more, but that has to be declared at the pump.

Generally, the Stromberg carbs are excellent (only one or two moving parts) but they are not infallable to the vagaries of time and fuels!

Hope that helps,
Rob

* Are you sure it's not a leaking gasket, the one between the two halves of the body? Remove the lower cowl to see and feel.
By thegasguy
#1817679
My experience years ago with old motorcycles leads me to believe that a leaky float that fills with fuel leads to uncontrolled flooding and very rich running - if not so rich that the engine won't even keep going.

Maybe it's that ? Not so sure as yet.

I've read of the Delrin and Neoprene issue; I've no idea which I have,but, as I've mentioned it's worked perfectly on English, French and Belgiumish Avgas and Mogas for years, so I reckon it's probably ok to assume it's the right stuff.

I've got my fuel from the same pump at the same petrol station for years - so hopefully that's not an issue.
Could be different stuff in it I suppose.

I will check for the exact place the fuel emerges from ( if indeed it emerges again ).
When I saw it, it was dripping from what I think is the air inlet used on 'carb heat' - the vertical tubular bit directly under the air filter.

More info to follow.
By MikeW
FLYER Club Member  FLYER Club Member
#1818004
Rob L wrote:Do also bear in mind that up to 5% ethanol is not required to be declared; many other Mogas fuels contain more, but that has to be declared at the pump.

.


AIUI that is actually the reverse of the labelling rules.
E5 can contain UP TO 5% ethanol. This includes ethanol free fuel. There is no official E0 designation.
95 octane fuel will contain some ethanol, unless from a small supplier exempt from the rules, but super grade can be ethanol free.

Here is what Esso say:

The majority of unleaded 95 Octane petrol sold in the UK contains up to 5% ethanol as required under the Government’s Renewable Transport Fuels Obligation (RTFO).

There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 and 99 grade petrol).

Esso super unleaded petrol (Synergy Supreme+ Unleaded 97 and Synergy Supreme+ 99 ) is ethanol free (except in Devon, Cornwall, the Teesside area, Scotland and NW England). We would therefore advise anyone who has concerns about the presence of ethanol in petrol to use Synergy Supreme+ – providing they do not fill up in Devon or Cornwall, the Teesside area, Scotland or NW England. The European standard BS EN228 covers the requirements for 0-5% ethanol unleaded petrol, the labelling requirement for zero % ethanol is E5 (as is up to 5%), a E0 label doesn’t exist. We understand that this is confusing if you are looking for zero % ethanol fuel, but as advised we can confirm that our Supreme Unleaded fuel supplied in areas except those listed (Devon, Cornwall, Teeside, Scotland and NW England) is ethanol free.
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By mick w
FLYER Club Member  FLYER Club Member
#1818060
Paul_Sengupta wrote:
MikeW wrote:(except in Devon, Cornwall, the Teesside area, Scotland and NW England)


Has anyone ascertained why these areas have ethanol in their "Super" unleaded?


If not taking into account the geographical spread , one might assume it's from a different 'Brewery' . :?
By MikeW
FLYER Club Member  FLYER Club Member
#1818111
I've no idea why the Esso varies regionally. Whatever the reason, it's a pity that no other supplier gives such information as far as I can find.

During the brief period I was able to fly last year I was using Tesco Momentum 99 - which also has the E5 label, as it must - from Lewes (East Sussex). I checked it each time and found it alcohol free. When I can fly again I will try it again.

In this area we have a small supplier which guarantees that its 95 is alcohol free. They are allowed to do this because of their low volume. They put an E0 sign on the pump (as of last October anyway) but it's unofficial, it should be marked E5. Crazy! Unfortunately they only have 95 not super.