Large Fuel Leak From Carb

[FlyingMonkey]

So I had a bit of a scary, eye-opening situation this evening.  I was at the hold short line at my home airport, preparing to depart, when I smelled fuel.  I shut down to investigate, and saw fuel coming off the bottom center of the firewall.  I took the cowl off and saw fuel literally pouring off the underside of the airbox.  After more investigation, I determined fuel (a LOT of fuel) was running from the left carb, back down the intake tube and into the airbox. 

Getting the airplane back to the hangar was an ordeal, so I won't get to investigate until tomorrow.  Any ideas on this?  It seems either the floats have to have completely sunk in the bowl, or the valve in the carb is stuck wide open.  I don't think it's the floats; whenever they have been heavy in the past, I get fuel running past the bowl gasket and into the drip tray.  In this case the drip tray was dry, and I just replaced the floats with the latest revision floats earlier this year. 

Has anybody ever seen anything like this before?  Seems like something that should not happen.

[GrassStripFlyBoy]

I've not experienced this, have a thought - but sounds like you had something bigger than this theory, I'd recommend reaching out to Lockwood or LEAF.  With drip trays dry expect the float level is fine.  The path to air box would be going by the needle and seat?  It may be a piece of debris, or possibly needle or seat is damaged, allowing fuel to pass by.  But if engine was running airflow and fuel draw might have just resulted in being a bit more rich and you'd not have really noticed this, more of an issue with plane parked and engine off?  Being it was running, yeah that's scary stuff.  

Or maybe something really crazy happened like the starting circuit jet came out allowing some massive uptake in fuel draw, those are screwed into the bowl, easy to check if present and tight.  But that might only be an issue if choke was on? 

[FlyingMonkey]

Thanks Darrell, I'm thinking along similar lines.  I took a fuel sample before leaving the hangar, and the fuel was dead clear as usual and there was no detectable fuel leak at that time with the fuel valve on.

Not sure what to make of this, I'm heading out this morning to investigate, and I'll take lots of pics and maybe a video or two.

[Tom Baker]

Did you replace the float needle at the rubber replacement? While not on the Rotax rubber replacement list I was told by Lockwood that they will start having issues after 6 or 7 years. Now I had a leaking float valve once, and it did the same thing with fuel running out the airbox. This was right after a carb service with replacement of the float needle, and I couldn't do anything to stop it. I sent the carb to LEAF, and they did something to the valve seat. They said it was a secret fix. I suspect it involved machining of the valve seat.

[FlyingMonkey]

Thanks Tom.  I replaced the needle when I rebuilt the carbs a couple of years ago.  But I found the problem...

The pin for one of the floats was slightly bent, and the float bound up against the wall of the bowl and wasn't moving.  I bent the pin back true (it's not overstressed, still very rigid), and did a run up and everything is fine.  After the run up I popped the intake tube off the carb and it's dry inside the tube and the carb inlet.

I think it's fixed, but do the experts among us feel that replacing the bowl assembly is a wise move, or is just resetting the pin a good fix?  BTW I inspected the floats and they don't have any damage, I flipped them upside down just so any abraded area I couldn't see would be on the side that would be least likely to contact the wall.  The offending float bound up at the top rear corner of the float.

 

The poorly narrated video:

https://photos.app.goo.gl/vUnWYQsmhz3L6pjs6

[Anticept]

There is a procedure if i recall for removing and resetting the pins. I think it was a service instruction, but maybe it was a bulletin. It was in response to some needles backing out.

Whenever I inspect, I try to remove the bowls with fuel still sitting in them, and ill give the floats a little tap to make sure they bob freely.

[FlyingMonkey]

I do the same "tap & bob" when I have the bowls out.  I think this happened when reinstalling the bowl, so there's no way to catch it until the *next* time the bowl is dropped. 

I think the pin is tight in its hole in the bowl, it was just bent a bit.  I think it's okay since I bent it back straight, just wondering if there is a compelling reason to do anything more or call it good.

[GrassStripFlyBoy]

I don't think this compelling, the stresses of bending and straightening are minimal - but if that pin loosens and comes out then it's a leak.  My bowls had some light corrosion so I replaced with the newer closed boss design under the pins.  A pair cost close to $300 as I recall, but as we often state - doing the work ourselves here I'll happily spend money on just the parts.

[FlyingMonkey]

Good point Darrell.  I have epoxy under the pins on the outside of my current bowls, so a loose pin should cause a minimal seep and not the stream I saw when I had one fail before. 

If the latest version is solid under the pins, that's a big enough upgrade combined with this pin being potentially suspect to justify the expense to me.  I replaced the other bowl with the open pin type a year or so ago, so I will probably leave that one in place for now and plan to update it later.

Now if we can just convince Rotax/Bing to thread those pins in the bowl instead of press fitting them, the bowl setup will be ideal!

EDIT: I just looked at prices and CPS has the bowl assemblies for ~$79 each.  That's about half what I expected.  I guess I'll replace both of mine at that price and be done with the concern of a loose pin causing a leak.  Does anybody know the part number of the improved bowls, so I can make sure I don't get shipped the old style?

[Jacques]

https://www.cps-parts.com/catalog/rtxpages/15-03762.php

963230 would be the right #, according to the latest (2018) Parts manual

same # as the 2016 manual  , but different from the 2011 manual

[GrassStripFlyBoy]

This is what I purchased from LEAF, more like $200 range total:

[FlyingMonkey]

Both CPS and Spruce list them at $79.  I think LEAF is usually more expensive for parts, in my experience.

[Anticept]

You don't need new bowls if you have an epoxy plug. Just check them with each inspection. Or, in your case morden, i'd even suggest a little solder/brazing plug. Easy to heat and take back out if you need to.