Cold wx starting quirks

Usually the carbureted Lycoming O-320 in my Skyhawk is easy to start.
But when it gets cold (below freezing), often the first crank yields
nothing. Not even a hint of a kick regardless of how long the starter
is engaged. Doesn't matter how many shots of prime are in there either
(in cold weather I normally use 3 or 4). The "trick" I've found that
works is to wait 5-10 seconds after disengaging the starter, NO
additional priming, then engage the starter. Usually starts in two or
three blades. In the rare instances that the engine still isn't
started at this point, I'll add a couple more shots of prime and try
the same sequence again.

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.
Jim Rosinski

Jim Rosinski 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.
Jim Rosinski

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.

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.

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

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

"G.R. Patterson III" writes:

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

Gaius Cornelius Tacitus, Roman senator and historian.

Ain't that the truth. Those old Romans knew the score. I just got
zapped with some lawyerly timidity this week at work which is putting
a cramp on developing a world-class estuary model.

In article ,
G.R. Patterson III wrote:

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.

I noticed that some time after I got my Comanche I had trouble starting
it. I finally realized that I had just gotten too fast at the start
procedure after doing it so many times. In particular the IO-540 seems
to benefit from at least a 2-3 second count with the fuel pump on after
you go to idle cutoff and a few seconds for the fuel to evaporate after
priming. The "symptoms" of doing the procedure too fast were basically
like the original poster described -- nothing doing on the first crank.

--
Ben Jackson

http://www.ben.com/

Us old farts know that the best cold wx start procedure for reluctant
engines is to prime it, verify that the mags are off, verify brakes or
chocks on, verify throttle closed, get out and pull the prop through
the magic number of blades -your choice but 6 blades works for most
folks - pull it through with a snap whipping your hands back and clear
each time as though you were starting it, just in case it fires... By
now the gas is well vaporized and sucked through out the induction
system... Get back in, mags on, half inch of throttle, and crank it...
This procedure will save the battery, save the starter, save the ring
gear, and save on four letter words...
Of course, one can also overhaul the mags with special attention to
bringing the impulse spring up to snuff, new plug harness, new plugs,
an RG battery for brisk cranking and experiment so that you know the
optimum number of primer strokes, and not have to get back out in the
cold (my choice being an old fart)

Cheers ... Denny

That's exactly the procedure I was taught when flying out of Pgh's AGC.
Brings back memories.

My experience is that each of these engines and engine installation configs
can be a bit different relative to cold temp starts. The POH doesn't always
have it. Not losing the battery charge is its own reward.

"G.R. Patterson III" wrote in message
...

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.

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.

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

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.

Gad, you guys use a lot of prime and throttle! I'd be afraid a
backfire would wreck the intake air filter. This is what I do:

First bow to the East and say two Hail Marys. Every aircraft is
different.

A trick I've learned (using mostly autofuel in a 172M) is to shut off
the fuel before shutdowns to empty the carb bowl - at least if it is
going to be sitting for a few days or more. Fresh fuel really helps
post-start running.
Be aware though that if the fuel shutoff isn't total, it will present a
treacheous safety problem if you somehow forget to turn the fuel on
again after a restart. It may, for example leak enough to allow
startup, taxi, and maybe even runup, but not support a takeoff. A
variation of this happened to me once with ice crystals in the
gascolator.

In a Minnesota/Wisconsin winter, I use 1 full prime preshot & hand prop
4 or preferably more blades before rolling out. I do the hand propping
with the mixture rich and the throttle completely closed. This helps
flash/vaporize the gas in the intake manifold due to the reduced
manifold pressure and the high air velocity across the idle port on the
throttle plate. Admittedly the engine may fire if some reason, the
mags don't ground out with the ignition switch. I don't have any
answer except to check for hot mags before shutting down earlier, and
to always be prepared for a hot prop.

Then I do a half shot prime during cranking and it gets me an immediate
lightup in one or two blades on my 172M. The second half of the prime
might be needed after a few seconds of running. Again, rank on a
nearly closed throttle (maybe 1/8 inch?) to help any fuel to flash in
the intake manifold. Three hands help.....

Adding taxi power for the first several minutes after starting with
autofuel causes a slug of fuel that has pooled in the manifold to go
thru the engine. When the engine is warm this won't happen.

Semi synthetic oil really helps. Any A/C with summer weight oil MUST
be preheated to get the oil viscosity within a safe operating range
before starting. Oil preheat on Lycomings, with the high camshaft
location, is really necessary. Even with the right oil, I get an oil
pump cavitation noise below about 32 deg F that tells me I'm pushing my
luck. Yes, the engine will start, but I suspect the post-start
lubrication is otherwise marginal, or worse, especially if it has been
sitting for a few days. Newer engines probably need preheat more than
old tired ones.

Take your time in taxi. The oil will be surprisingly slow to warm up
since the lub system of most engines has relatively little access to
the heat of the engine when the oil is cold and just blowing over the
relief valve. I know the manufacturers suggest otherwise, but they get
to sell rather than have to buy the repair parts.

Our '65 Cherokee seems to like 2 or 3 shots of prime before cranking, with
the primer left out during cranking. When the engine catches, slowly put the
prime in. I've tried variations with the above yielding the least cranking.
We do have Tanis heater and are hangered in a "heated" (read at least above
freezing...) community hanger.

We're hoping to fly the club's 182 to Indiana Christmas day & back the next.
Not sure, as cold as it is here. That 182 is hard starting cold. Yet to find
a good technique for that animal...


"G.R. Patterson III" wrote in message
...


Jim Rosinski 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.
Jim Rosinski

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.

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.

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