The Cessna 120-140 Association Forum

Trying to chase down where this slight leak is coming from. From the picture you can see stain on the cowl that appears like something has been dripping there over time. I wiped that area and surrounding cowl, after test flights that area comes back dry. The fuel mixture collects on the lip on the pressure bend of the cowl. Sometimes enough to show a small amount on a drip pan. The consistency and color of the liquid ( fuel) seems like it may be running from somewhere and mixing with old oil ? It is darker and thicker than say a bright blue leak from a fuel drain sump. The carb recently rebuilt and the carb fuel line connector is dry. Thoughts?

Fuel/oil mix dripping from the airbox?

Seems on shutdown I was getting a fair amount of oil draining back from the cylinders via the intake manifold, into the airbox, presumably because i had the wrong valve rockers on the intake side for one reason. Replaced the rockers with correct, rebuilt the carb at annual, aribox drip non-exisitent now. This cure was a Randy Thompson pearl of wisdom...

stromberg or marvel carb?

stromberg carb even when rebuilt is very difficult to get to consistently not drip with fuel on. even the stromberg specialist included in his logbook entries that you needed to turn the fuel off.

It’s a Marvel carb. MA-3SPA

Either take off the cowling or get in there with a light and mirror. The MA3SPA likes to leak from the drain plug and also the accelerator pump gasket. Those are two possibilities as well.

Found the leak. I’ve been meaning to look at the operation of the primer for several flights but did not get around to it till today. Turns out there is a tiny pin hole near where the line attaches to the cylinder. Sprays all over that area near carb and then leaks down to the area where I have seen it after flying. My guess is it might be leaking a small amount in flight but not sure. Either way needs to be replaced. I might have enough slop in line to cut above hole and re flare. If not does anyone a cheap route to get a new one or replace. Initial glance on internet …….expensive!!!
Mike

Mine is just copper line that I replace every 5+ years or so, not very expensive at all. There's a fitting I need to solder onto the end of the copper line where it goes into the atomizer/spider. Not sure what you have. Leak by cylinder?

Thanks for info. I may have said it wrong. Mine looks just like that… the little hole in my line is where your line looks dis colored. I think I have enough slop to re flare.

https://www.aircraftspruce.com/catalog/ ... -40900.php

There shouldn't be a flare. It should have a ball shaped fitting on the end.

There is no flare, you un-solder this AN800-2a from the copper tubing And re-solder onto the new tubing, remembering to put the nut on the tube before you solder.

It all fits into the atomizer If you don't know the history of the copper tubing you might just replace it as it work hardens apparently. Cheap insurance. My IA showed me how to do this.

You probably have a 'flare' up by the firewall where the copper tubing connects where it goes thru the firewall.