Fuel Diagrams

[Big Pistons Forever]

For twin Cessna pilots my go to, to see if he/she knows the fuel system is to ask how many fuel pumps there are. The 340 I last flew was typical with a total of 10 pumps 2 mechanical and 8 electric.

For bonus points I ask how you can start it with a failed boost pump.

[Colonel]

Crossfeed is too easy. Pull the spark plugs and squirt gasoline in. Or ether into the air intake!

I used to prime a Kinner radial by putting gasoline in the zoomie exhaust stacks, then pulling it through. No primer on a PT-22!

[Slick Goodlin]

Crossfeed is too easy. Pull the spark plugs and squirt gasoline in. Or ether into the air intake!

I used to prime a Kinner radial by putting gasoline in the zoomie exhaust stacks, then pulling it through. No primer on a PT-22!

No accelerator pump in the carb? The two Kinners I’ve been around (but tragically never got to fly) had them.

[Colonel]

That works too but always made me nervous… one person pulls the engine through while another person sits in the airplane and pumps the throttle when he sees the prop move.

Updraft carburetors are at risk of fire. You hope you get lucky.

PS only prime the top cylinders on a radial. I have seen a plunger-type primer added to the side of a Kinner cowl and it was plumbed to the top cylinders.

[Colonel]

Look under the cowl at your primer lines. Even a simple carbureted Lycoming may have one, two or three cylinders plumbed. It’s kind of random. The more cylinders primed, the easier it is to start. Remember when you’re cranking only the left magneto is firing - just one spark plug (on a Lycoming ... the big Continentals use two impulse coupling mags IIRC and are easier to start because of it).

If you were careful you could get a good start on an old 172 by pumping the throttle ONLY while you were cranking to pull the fuel into the engine from the updraft carburetor. Unlike the primer, all cylinders get fuel and that gives you a better start.

You screw it up, you can get quite the fire going in the intake. Best keep cranking when that happens.

Fuel injection has the advantage of priming all cylinders but fuel can still run out the intake and cause a fire. My kid used to do that so much, we were going to rename him Torchy. True story.

Also you can hydraulic lock too. Down the road people discover bent connecting rods and can’t figure out why. Big Continentals seem to do that.

Anyways, the colder it is, the more prime you need because fuel evaporates slower as the temp drops. Run mogas if you can, pre-heat and definitely move someplace that never gets colder than 60F and W100 is your winter weight oil (W120 is my summer weight oil - works better when the oil temp is over 180F).