Carb Float Bowl Breather/Overflow

"All my clients have fuel heat shields / drip trays so fuel is easy to see. I do get guys in here that have fuel in their drip trays, but I can usually fix that by either replacing the rubber gasket or just repositioning it."

heat shields - Good policy Roger. I don't have them - may fit "down the track"

drip trays - Sorry! I cant see a drip tray, heated by proximity to engine/exhaust, subject to vibration/ large movements and bathed in warm high speed air, ever having any evidence of a fuel leak in it, unless the leak is very large and continues right up to engine shut down. 

Drip trays, in this situation, make very little sense to me. What do they actually achieve? In the dynamic environment of the engine bay, very unlikely to contain a large (fire potential) leak and don't show small leaks. Pilot may feel good/piece of mind but I think its probably illusory.

The only reliable way to know if the float bowl is venting fuel through the breather, is to install a catch can.

I make my temporary diagnostic fuel catch cans out of my granddaughters small fruit juice "popper" plastic bottles. Drill a hole in the top for the tube and some smaller "breather" holes around the "neck" & secure with cable/zip ties - works a treat!

Hi Sean,

I have seen a ton of planes come in with live fuel in the drip trays (heat shield)  especially with the older fiber gaskets. Some trays are cupped somewhat and some fairly flat, but even the flat ones had live fuel in them. This has been fairly common. Some of the drip trays have small drain hoses fitted to them to route the fuel back down the fire wall closer to the cowl opening. The drip trays for engines out here are extremely common.

You'r the man Roger, so despite my reservations ( above), I believe you .

NOTE: my float bowl fuel emissions are exclusively from/through the breather tube - not spillage through badly fitted/damaged bowl seals.

When I was having needle seat leakage problem on one carb a lot of fuel came running out of carb throat and out the k&N and then wanted to drip on the muffler. I could see fuel coming up through the center jet and needle.  I have the drip trays under carb but most of the fuel did not go there. 

Since this thread concerns float bowls, perhaps my problem belongs here.  I just finished removal, disassembly, inspection, assembly, and reinstallation of my 2, 914 carbs.  I only replaced the O-rings and the 2 screws on each throttle valve.  The rest looked good, and my older Bing floats have never weighed more than 6 grams per pair, although my scale was not expensive and may be inaccurate.  I tried to start it today for the first time after re-installation.  I get almost no cylinder ignition - certainly not enough to keep it running.  However, I do get fuel running out of both drains.  My drains are set up so the airbox and carb tray lines join together on each side and then exit just below the firewall.  Both of these drains leak fuel.  In fact, I have to now turn off the main fuel valves to stop the flow after trying to start it and pressurizing the fuel lines.  I'm thinking perhaps one or both float bowls are flooding and the excess fuel may be running back into the airbox.  One of drip trays also shows fuel and the fuel line connector area appears wet with fuel also.  It's a tail dragger, so the airbox is lower than the carbs on the ground and fuel running back into the airbox appears possible.  My next steps will be to open the float bowls, leaky side first, and see if something has gone wrong.  I have a good idea of what to look for with the floats and bracket, but I'll be stumped for awhile if it's a float needle valve, because they looked good when I had them off.  I welcome any advice.