The issue with the PA-22 right tank fuel system was too many up and down routings of the fuel line from the right tank. ?The fuel came down the right side of the plane, then back up behind the instrument panel, then down to the fuel selector on the left kick panel, then back up again to the feed through on the firewall, then down to the gascolator and back up again to the carb. ?It was way too easy to get it air locked. ?I oversaw a PA-22 restoration in 2011. ?One of the many STCs we installed was a rerouting of the right fuel line to pass under the front seat to elminate some of the up and down loops.
I ran into a similar issue on a Taylorcraft last month. ?From the time the owner bought this plane, it has had an unnervingly intermittent issue with running out of fuel and shutting down either while warming up, or about the time he started his take off roll. ?This is a really simple fuel system with a header tank feeding through a shut off valve through the firewall to a gascolator, then back up to the carburater. ?What could possibly go wrong in such a simple system and how could the owner have this going on for the last 8 years without finding a solution? ?When I looked at it, I noticed that it had modern integral firesleeve fuel lines between the fuel tank and gascolator, and from the gascolator to the carb. ?Both lines were a bit longer than necessary, so each made a very gentle up and down loop in the hose routing. ?So, there was an up and down loop between the tank and the gascolator, and another up and down loop between the gascolator and the carb. ?That created two air traps, so if he had his fuel shut off and sumped the gascolator, he would trap air in the system and create an air lock either between the tank and gascolator, or between the gascolator and carb. ?Even with a full tank of fuel, the lines would air lock and stop the fuel flow. Lesson to learn here is to be very careful about the up and down routing of your fuel lines. ?Make the gascolator (if you use one) the low spot in the system, but don't create additional up and down runs expecting gravity to feed properly. ?It only takes a small bubble of air in the line to stop the flow even with sufficient head pressure to feed. ?Ram air pressure into the tank is one way to push the bubble through. ?But be careful to make sure your ram air is always going to be ram at at all speeds. ?That's a mistake I made on my KR that created one of the strangest fuel system failure modes I've ever seen and took me nearly 2 years to isolate and fix. -Jeff Scott Los Alamos, NM > ----- Original Message ----- > From: Craig Williams > Sent: 04/07/14 12:12 PM > To: KRNet > Subject: KR> Ram air fuel venting > > Has anyone used RAM air to vent thier tanks? > > Funny how things pop up.? I asked the question here a few days ago about > having two fuel pickups and then came upon this article.? It addresses an > issue with RH tanks in the PA22's but I think it has relevance to our KR's.? > I actually had an elaborate venting scheme for my 4 fuel tanks but after > reading this I am inclined to go the RAM air route, at leat on my mains.? > Should make the fuel pumps job easier too. > > > Here is the article that explains: > > > kr2seafury.com/resources/Pages+from+SWPN-April-May-June-2014.pdf > > Craig
