Cold wx starting quirks

G.R. Patterson III wrote:

Be darned if I know why this (waiting between cranks) works, but it
does. If anyone knows why or even has a theory, I'd love to hear
it.

You're hitting the primer before cranking? That loads the induction
system with
raw gas, basically flooding the engine. When you wait a bit, some of
that gas
vaporizes and the engine starts more easily.

Yup that's the technique I've used, and matches the POH instructions.
Are you saying the primer can't do its job (atomizing the fuel) unless
you're cranking while priming? Is priming without cranking the same as
pumping the throttle?

Try this. Pull the primer back but don't prime the engine. Hit the
starter and
while the starter is turning the engine, give it three shots of
primer. On real
cold days, it may take four. That gets my O-320 going every time.

OK I'll try that and see if it helps (e.g. by giving a first-crank
start). Though the primer goes pretty hard and it'll take quite a few
blades to get 4 shots in there while cranking. What I have tried in
the past that didn't help is priming while cranking AFTER the first
failed crank. But if you're right and the engine is already flooded
from the first prime, it would make sense that additional priming
wouldn't help.

Jim Rosinski

Jim Rosinski wrote:

Are you saying the primer can't do its job (atomizing the fuel) unless
you're cranking while priming?

Yep.

Is priming without cranking the same as
pumping the throttle?

Sort of, but there are differences. Pumping the throttle squirts a jet of gas
into the carburettor. The primer ports are located further into the manifold. In
my engine, I have two and they are located immediately before two of the
cylinders. Priming while cranking causes the gas to be drawn into those
cylinders. Priming before cranking allows it to run down into the manifold under
the engine.

My plane is a tailwheel aircraft, and the carb is behind the engine, so pumping
the throttle basically puts a pool of gas into the manifold behind and below the
engine. Doesn't work for a cold start for me -- might for you.

George Patterson
The desire for safety stands against every great and noble enterprise.