Priming

Disclaimer: We have no professional or expert qualifications of any kind.
It's fully up to you to check any information you find here with
standard aviation industry sources such as aircraft maintenance
manuals, flying instruction books and, above all, FAA regulations!

 

By Ed Burkhead

On the ercoupe-tech forum, we had a discussion about the desirability of a fire extinguisher in the plane and perhaps another outside, just in case a fire starts in the engine compartment during the startup attempt.
http://groups.yahoo.com/group/ercoupe-tech/

Points brought up:

1.  If you do have an engine start fire, keep it cranking to, hopefully, draw the fire into the engine where it belongs.

    a.  Corollary:  It's good to have a battery that's not old and worn out so you can keep cranking the engine a while.

2.  Have a fire extinguisher or two in easy reach. It may be good to have one outside the plane as you may not want to mess with unclipping a fire extinguisher before exiting the plane.

3.  Priming   (the reason for this page)

It was always my habit to give the engine one or two shots of prime if it was cold, then start cranking.  Usually, after doing so, the engine would start fine.

If it still wouldn't start, I'd pull the prime out, start cranking and slowly push in the primer just fast enough to keep the engine running.  By the time the whole primer shot was in the engine, the engine was almost always running.  If the engine started before I had pushed the primer in fully, I'd continue pushing it in quite slowly till the primer was empty and locked.

The downside is that sometimes others have had the engine catch fire from a backfire when they injected the fuel before they started cranking the engine.  One person described watching the front of his plane burn up.

John Cooper responded with, "It is my practice never to use the primer if the engine is not already turning over. That way there is little tendency for the fuel to end up other than in the cylinders."

John later wrote, "Look at it this way: what good is fuel to an engine that is not turning over?  Worst thing that will happen is it will start before you get the 2 shots [of primer] in (pretty likely).

"
You can get away with priming first on engines that have the primer nozzles in the intake elbows as most of the fuel ends up in the chamber around the intake valve.  Continental C-series have the fuel nozzle in the intake just above the carb.  Fuel introduced here has a strong tendency to fall down into the carb and then into the air filter box."

Speaking as myself, again, I think I'll adopt John's procedure in the future.

This is not holy writ.  Just use this as the starting point in researching and deciding on your own procedures.
 

In flight engine failure

And, a final note.  If the engine stops in flight, many people have kept the plane in the air all the way back to the airport using the primer to provide fuel to the engine.

I knew one guy with a mysterious in-flight power loss problem who used the primer to get back to an airport several times before the problem's cause was found. I'd strongly recommend finding the cause of any engine failure before flying again and he tried but it bit him several times before he finally cured the problem.  This technique got him back to the airport each time.)

If I've read the aviation lore correctly, more engines stop from fuel system faults than from anything wrong with the engine.  You may want to try the primer.