A hot start question

Hi peoples.. Hopefully this is an easy one for you experts out
there...

Hot start on a fuel injected Lycoming commonly seems to call for
leaving the mixture at ICO and cranking. Bearing in mind the engine
stopped because the mixture was set to ICO, and if you're then not
moving the mixture before cranking, how does the engine then fire??
What's in there for it to fire??? Shouldn't the same lack of fuel
that caused it to stop also prevent it from starting again??

Are we saying the injection system leaks after the engine is shut
down?? And is that dribbling from the injectors what causes
flooding??

Cheers

Chris

chris wrote:
/snip/

Are we saying the injection system leaks after the engine is shut
down?? And is that dribbling from the injectors what causes
flooding??

Cheers

Chris

Chris,

That is *precisely* what we are saying! Now, the subject of how to best
re-start said hot injected Lycoming is on par with the greatest
political and/or religeous discussions of the ages, but here's my 0
cents worth:

Since we are, in fact, presented with a flooded engine, per se, the idea
that one should turn "on" the boost pump during this procedure, thus
shoving *more* fuel past the leaky flow divider and in to the cylinders,
is counter-productive. When the engine was last shut down, the throttle
was set at a nice idle RPM. LEAVE IT THERE, and leave the mixture in
cutoff when you start to crank. As the engine begins to fire, advance
the mixture to full, then back to "ground lean". If, after running, the
engine begins to falter, THATS when the boost pump may be required to
purge vapor out of the lines. This procedure produces nice, smooth hot
starts, with none of that 3000
RPM-panicky-grab-the-throttle-quick-before-we-go-flying-into-the-next-tiedown-row
BS that a lot of procedures seem to produce. IMHO, YMMV, yada yada...

Happy Flying!
Scott Skylane

On May 11, 2:45 pm, Scott Skylane wrote:
chris wrote:

/snip/

Are we saying the injection system leaks after the engine is shut
down?? And is that dribbling from the injectors what causes
flooding??

Cheers

Chris

Chris,

That is *precisely* what we are saying! Now, the subject of how to best
re-start said hot injected Lycoming is on par with the greatest
political and/or religeous discussions of the ages, but here's my 0
cents worth:

Since we are, in fact, presented with a flooded engine, per se, the idea
that one should turn "on" the boost pump during this procedure, thus
shoving *more* fuel past the leaky flow divider and in to the cylinders,
is counter-productive. When the engine was last shut down, the throttle
was set at a nice idle RPM. LEAVE IT THERE, and leave the mixture in
cutoff when you start to crank. As the engine begins to fire, advance
the mixture to full, then back to "ground lean". If, after running, the
engine begins to falter, THATS when the boost pump may be required to
purge vapor out of the lines. This procedure produces nice, smooth hot
starts, with none of that 3000
RPM-panicky-grab-the-throttle-quick-before-we-go-flying-into-the-next-tiedo*wn-row
BS that a lot of procedures seem to produce. IMHO, YMMV, yada yada...

Happy Flying!
Scott Skylane

That makes sense to me!! I had wondered how it all works, and now I
think that since I understand it a lot better, I am in a better
position to know what to do.. Since I began flying injected engines I
so far have not had a engine that wouldn't start when started
according to the book, but the time will come!!!

Lycoming seems to be the worst to start in these situations. I have an
IO-520 and have similar problems. First off the vapor lock is not in
the spider lines sitting just above the engine. The vapor lock is in
the engine driven fuel pump. Mixture at cut off and run the aux pump
for about a minute. This will run cool fuel thru the engine driven pump
and then back to the tank. The last five seconds that you are doing
this push the mixture control in and leave it there. That allows the
fuel to now go into the spider lines. Throttle all the way out. Start
cranking, while slowly advancing throttle. About 1/2 way in engine will
fire and run. Adjust throttle for about 1000 rpm. If engine wants to
stumble because you let off the starter at the wrong time bump the aux
pump for about 1 second at a time. Never had to do this more than twice
to keep engine running. I very rarely have to bump the pump and get
successful starts about 95% of the time when the engine is hot.





chris wrote:



That makes sense to me!! I had wondered how it all works, and now I
think that since I understand it a lot better, I am in a better
position to know what to do.. Since I began flying injected engines I
so far have not had a engine that wouldn't start when started
according to the book, but the time will come!!!

On May 11, 3:28 pm, Newps wrote:
Lycoming seems to be the worst to start in these situations. I have an
IO-520 and have similar problems. First off the vapor lock is not in
the spider lines sitting just above the engine. The vapor lock is in
the engine driven fuel pump. Mixture at cut off and run the aux pump
for about a minute. This will run cool fuel thru the engine driven pump
and then back to the tank. The last five seconds that you are doing
this push the mixture control in and leave it there. That allows the
fuel to now go into the spider lines. Throttle all the way out. Start
cranking, while slowly advancing throttle. About 1/2 way in engine will
fire and run. Adjust throttle for about 1000 rpm. If engine wants to
stumble because you let off the starter at the wrong time bump the aux
pump for about 1 second at a time. Never had to do this more than twice
to keep engine running. I very rarely have to bump the pump and get
successful starts about 95% of the time when the engine is hot.


That sounds a bit different - mixture rich for a hot start?? Is this
because it's a IO520??? I am using a IO360 in an Arrow, if that makes
any difference..

Now reading this I remember when I was a passenger in a Twin Comanche
a few times and the engines on that kept trying to die just after
start and the pilot had to give it a blast of boost pump a few times
until it stabilised..

chris wrote:
This will run cool fuel thru the engine driven pump
and then back to the tank.

This works for me on the IO-550.

Cold start is: Mixture rich, throttle cracked, boost pump on, pressure
comes up, boost pump off, clear prop, crank

Hot start is the same except the boost pump is run much longer before
attempting to crank.

Actually, hot starts are only an issue if you shut down, go away for
a while and try to start up (the worst case is your average fuel
stop). The thing starts right back up again if you crank it up
after it was running (good thing too if you run a tank dry).

On 10 May 2007 20:44:03 -0700, chris wrote:


That sounds a bit different - mixture rich for a hot start?? Is this
because it's a IO520??? I am using a IO360 in an Arrow, if that makes
any difference..

It makes all the difference in the world. You have Bendix/RSA fuel
injection that does NOT have a constant displacement engine driven
fuel pump and that does NOT have a return line to the fuel tank.

"Classic" Continental fuel injection is a different...

BTW, it's easier to add a little more full if you need to than it is
to clear a flooded engine. Sounds like you've got it figured out.

TC

On May 10, 10:16 pm, chris wrote:

Hot start on a fuel injected Lycoming commonly seems to call for
leaving the mixture at ICO and cranking. Bearing in mind the engine
stopped because the mixture was set to ICO, and if you're then not
moving the mixture before cranking, how does the engine then fire??
What's in there for it to fire??? Shouldn't the same lack of fuel
that caused it to stop also prevent it from starting again??


In my experience, the six cylinder Lycs are bitchier during hot starts
than the fours. The only Conti experience I have is with the Baron and
those engines seemed easier to start hot than Lycs.

Chris,
It seems like you're getting plenty of Continental tips, this is what we do
for the IO540's in our Aztec. Aztec's are known for difficult hot starts
due to their tight cowlings that rap their IO-540 Lycoming engines. Only a
week ago a fellow Aztec driver arrived at STE and refused an immediate
refueling because he could never get it re-started when hot. The following
is our method and it hasn't failed us yet.

Throttles full open.
Mixtures full rich.
Boost pumps on ONLY until you see the slightest movement from the fuel flow
indicator.
Immediately turn pumps off, mixtures idle cut off, throttles off then
cracked open. Now crank.
While we crank we can watch the compression build as the prop slows
slightly, within the next full turn the engine will fire.
As the engine fires, mixture up to ONLY 1/3-1/2 position.
Hand back to throttle to jockey it slightly if the engine stumbles.

One point that I try to enforce when teaching students about hot starts is
to remind themselves about the density altitude INSIDE the cylinder, where
combustion takes place. The correct fuel/air mixture "window" is relatively
small but this is your goal. Hot engine, thin air... it won't take much fuel
to reach the proper mixture for combustion.

Some POH's, including the Aztec's advocate putting the engine into a "known
condition". Basically intentionally flooding the engine and then cranking
to pump air through the cylinders until the additional air added to the
excess fuel finally brings the overly rich mixture down to combustible
level.

When I gave air rides in an Archer with a typical O-360, I would simply
start with the throttle at idle, mixture rich then as I cranked pulled the
mixture towards idle cut off. Without fail it would fire right up as I
reached about 1/2 position on the mixture.

Jim

In a previous article, chris said:
Hot start on a fuel injected Lycoming commonly seems to call for
leaving the mixture at ICO and cranking. Bearing in mind the engine

That's how we start our Lance's IO-540 both hot and cold. Leave the
mixture, prop and throttle exactly where they were at shut down. If cold,
turn on the electric fuel pump and open the mixture for a few seconds to
get some fuel into the cylinders and then back to ICO. Crank, and as soon
as it catches, mixture to full rich until it stops sounding like it's only
running on a couple of cylinders, then lean.


--
Paul Tomblin http://blog.xcski.com/
O Canada, we stand ready to sit down and discuss our problems
in a civilized fashion for thee.
-- wednesday