Why do Lycomings start lean?

[Ilikeflying]

Hi Everyone.

Im just wondering if anyone knows why the Lycoming start process involves cranking while mixture is in the idle cut off position, and advancing the mixture when the engine kicks over, as opposed to Continental where it is started in the full rich position.

In my mind there really doesn't seem to be a lot of benefit in having the throttle in by some made up amount, resulting in the engine revving up way past 1000 on a cold winter morning in the time it takes to get your hand from the mixture to the throttle.

I'm just wondering what might be the reason for this starting process.

[Lead Balloon]

What model Lycoming engine are you comparing with what model Continental engine?

Some Lycomings are fuel injected, and some are not.

Some Continentals are fuel injected, and some are not.

The 'standard' Lycoming fuel injection system is a 'mass airflow' system.

The 'standard' Continental fuel injection system is a 'continuous flow' system.

This is one of the reasons for the inherent dangers in the old wives' tales that circulate.

[Ilikeflying]

Sorry, say the Lycoming IO-540 typical of perhaps a Cherokee Six, vs the Continental IO-520, typical of a 210.

[Lead Balloon]

Roger.

You will learn lots if you do some research on the 'standard' fuel injection system fitted to Lycoming injected engines and the 'standard' fuel injection system fitted to Continental engines.

They are different.

This might explain the different starting methods.

Let us know what you find out. :ok:

[Sunfish]

Ilikeflying:

In my mind there really doesn't seem to be a lot of benefit in having the throttle in by some made up amount, resulting in the engine revving up way past 1000 on a cold winter morning in the time it takes to get your hand from the mixture to the throttle

If that is what happens to you, then you aren't doing it right. Try a little less throttle (1/4 inch starting point) and you should end up with the rpm around 1000 - 1200 just after it catches.

At least on the C172 I am occasionally privileged to fly, that is what it does after about Five blades.

[roundsounds]

You could also do yourself a huge favour and track down a copy of the Lycoming Flyer Key Reprints. This document consists of a collection of operating tips by Lycoming staff.

You'll find lots of links on the web, here's one I found:

http://www.lancaironline.net/bookstore/lancair/lycoming_flyer.htm

http://11hc.44rf.com/manuals/engine-prop/lycoming/lycoming---flyer_key_reprints.pdf

[Ixixly]

roundsounds, the Airvan is Lycoming powered and most certainly does call for Mixture ICO to start. This is the only properly Lycoming powered Aircraft I've flown though, had a couple here and there changed over so obviously the POH didn't reflect the different engine but I still start the Lycomings with ICO and Continentals with Mixture Rich and haven't encountered too many issues (At least none that I'd attribute to the engine rather than my own mistakes!).

[Left 270]

Leadie,

Do you know of any good publications on the subject? I'm interested myself and know the Conti way of doing things but not the other too well. I've had a google but haven't come up with much credible info. Cheers.

[ForkTailedDrKiller]

God, you see some crap on here!

Every fuel injected Lyc I can recall, and yes I have flown a few over the last 40 yrs, starts (cold and hot) with the mixture in idle cut-off - by the POH.

Why? Dunno - who cares - it works!

I fly lots of different aeroplanes, mostly post-maintenance test flights. Some types I have lots of time in, some very little or little recent time, and some I have never flown before (ie Expedition 350 - look it up - there is only one in Oz).

http://www.northwestbackcountryaircraft.com/siteart/gallery/expedition/2sm.jpg

If in doubt - do it by the book - generally works fine for me!

Dr :8

PS - There is an exception to every rule, and in this case it is hot starting an IO520 Bonanza with a single speed (high) fuel pump! :E

[27/09]

Ilikeflying: In my mind there really doesn't seem to be a lot of benefit in having the throttle in by some made up amount, resulting in the engine revving up way past 1000 on a cold winter morning in the time it takes to get your hand from the mixture to the throttle.


You should have your hand on the throttle during the start not the mixture.

As the engine fires set the RPM with the throttle then set the mixture to full rich. This way there is no excessive revs as you start.

The engine will run for several seconds before you need to advance the mixture.

The method I use for a Lycoming fuel injected engine that works every time is,

Cold start :

Set full throttle and mixture
Prime till fuel flow gauge rises and stabilises
Mixture to Idle Cut Off
Set Throttle to idle
Hand on throttle and crank engine.
As engine fires up set RPM
Mixture to Full Rich

From a cold start I've never known an engine not to start first time using this method.

Hot Start
I find hot starts are not generally as easy as a cold start.

The need to prime depends on how long since shut down.
If it's only a couple of minutes I don't prime at least initially.
If in doubt don't prime for the first attempt
If priming is required prime till fuel flow gauge starts to rise.
Mixture to Idle Cut Off
Set Throttle
Start cranking while slowly advancing throttle (go to full throttle if necessary but be ready to close it back to idle as soon as the engine fires).
As engine fires set throttle
Mixture to Full Rich

Don't crank for more than 20 seconds.

If the engine doesn't start first time, and you haven't primed to start with, prime till fuel flow gauge starts to rise.

[Jabawocky]

I have a pretty good answer, which is not backed by any documentary evidence, but is just from observation of the systems and the actual goings on in the systems…….but, I suspect another "non expert" on prune might like to explain it as we have discussed this matter before.

I am surprised he has not piped up yet.


27/09

May I suggest your cold / hot starts should be;

Cold start :
Set full throttle and mixture YES
Prime till fuel flow gauge rises and stabilises YES Or count 1-2-3-
Mixture to Idle Cut Off YES
Set Throttle to idleYes, or crack it just a fraction, idle may be a bit low (fully closed) so just about where you think 1000 RPM would be
Hand on throttle and crank engine. No hand on throttle, just on the mixture
As engine fires up set RPM As engine fires roll the mixture up….just about half way, usually no more then let the rpm settle and lean to just past peak ROM…Job done!
Mixture to Full Rich Never required on the ground until you line up to go :ok:
From a cold start I've never known an engine not to start first time using this method.

Hot Start
I find hot starts are not generally as easy as a cold start. They are easier (refer above and delete the prime), if it is a genuine hot start, say after land/refuel, simply leave the throttle in the 1000RPM idle/taxi position and crank, at the first cough roll the mixture in as per above.

you may need the boost pump after that if there are any vapour locks.


The need to prime depends on how long since shut down. Yeah and that usually is a few hours. 30 minutes is a hot start except for kiwi's in winter :E

Hope that helps! :ok:

[Stikybeke]

Uh Oh...

Best connect the GPU!!! I just know what's gonna happen now

Sticky
☔️

[yr right]

well at the point of making a point and I don't care what you all think this is how I do it for both lyc and tcm with injection


extreme cold
prime
get out of the cockpit
pull through the eng half a dozen times
crack throttle (small crack just over idle)
mixture ico
crank and on start slowly increase mixture to approx. half way.
as it clears increase to full mixture.
increase throttle as require to 1000


normal cold start
as above with out the pull threw
however you should always pull threw before any start.


if you have started and oil temp and engine is warm as above but just with a smaller prime. hand on boost pump if it requires more


most times my starts don't go over 800rpm and start 1st time every time unless there is a proplem


I never have to touch the throttle on start up


now I only start and run engines all but every day and more than once. so that's how I do I really don't care if you don't and ill guess ill get heaps of flack saying I don't know what im doing blah blah but when you start as many engines as is do well then tell me what to do.

[yr right]

just to add.


slowly increase the mixture, not fast not extremely slow to half way then then you will hear it clear.
start the right engine 1st


why
so you can hear it.


then the left
why
cause you can hear it cleaner because its closer to you.


you will notice engineers always start r/h then l/h




so today I started two c400 serries engines that 4engines in total.


the 1st aircraft 10 c oat normal cold start 750 rpm both engines


2nd aircraft approx. 24c 740 both engines on start




happy days

[Stikybeke]

I knew it!!!

....and here's silly me all these years thinking the RH Engine was always started first in case there was a fire in the engine on start up which would then mean exiting the aircraft past the unstarted (and not on fire) LH Engine which would be the safest way out.....

I'm glad that's all cleared up now....

Stiky
;)

[ACMS]

Yep and in the PA31 you started the right first after pushing down the gear lever to check the hydraulic pump........it's been 25 years but I think that was a procedure????
Someone will correct me I'm sure :ok:

[PA39]

The fuel lines are pressurised with the pump whilst the mixtures are at rich, pumps turned off and then mixtures to ICO before start, otherwise the engine (s) WILL flood!!

[27/09]

Jabba,

In my experience the injected Lycomings I'm most familiar with have been much much easier to start cold than warm. It's almost impossible to stuff up a cold start but I've seen plenty of botched hot starts. There's one flying school not far from here who's students seem to have no end of bother with hot starts on their injected C172's. However like anything YMMV.

Also I have a lot of experience with pilots new to an aircraft and or fuel injection and they tend to be ham fisted with starts usually having too much throttle set The OP also mentioned high RPM at start up. That is why I consider having your hand on the throttle instead of the mixture is a much better idea.

If you're flying that aircraft all the time then you'll know exactly where to set the throttle but there's a lot who don't.

There is no need to be in a hurry to advance the mixture.

I agree there isn't generally a need to go full rich until you're ready to roll.

[27/09]

ACMS: Yep and in the PA31 you started the right first after pushing down the gear lever to check the hydraulic pump........it's been 25 years but I think that was a procedure????
Someone will correct me I'm sure

Then on shut down, stop the right first and do the gear lever thing to check the hydraulic pump on the left engine before shutting the left down. :ok:

[ShyTorque]

Years ago I instructed / flew Lycomings, RAF fuel injected type.

I was led to understand that heat soak from the engine could cause expansion in the fuel system and fuel to enter the inlet manifold after shutdown, tending to over prime the engine. So deliberately restricting the fuel flow on start was a way of avoiding over enriching the mixture.

[Plow King]

Left 270

The Airframe and Powerplant Mechanics Powerplant Handbook produced by the FAA gives a fairly detailed explanation of the systems.

Powerplant Handbook

PK

[Jabawocky]

PA39

The lines up to the cylinder from the FCU contain no pressure once the mixture is at ICO.

OK, this is my observation of why it is the TCM and Lyc are different. In my opinion and observation a TCM will not pump much fuel at cranking RPM which is very very low. The overly rich situation eventually (and quickly) finds the right F/A ratio and lights off. The low RPM and thus low extra fuel delivery means no excess post-priming fuel will dribble in.

The Lycoming which is now primed up and overly rich, waiting for the F/A ratio to get optimal will start pumping fuel according to mass airflow immediately (and at the FR position this will be very rich….and will be too rich to start when combined with the primed amount.

Two different systems, two different techniques. :ok:

[Jabawocky]

27/09

It's almost impossible to stuff up a cold start but I've seen plenty of botched hot starts. There's one flying school not far from here who's students seem to have no end of bother with hot starts on their injected C172's.

I tend to agree, cold ones present less opportunity to stuff up. One is not harder, just some find ways to create that scenario.

I would bet your local school 172's are not being started exactly as I describe. There will be all manner of throttle positions, mixture, priming and hence the problems.

The engine, provided it has good plugs, good mags and a F/A ratio that is right, WILL start every time. No argument. The pilot controls the F/A ratio and assuming the engine is "conforming to spec" all you do is get the F/A ratio right.

Some Lycoming operators who apply a bit of TCM start procedure (seen this a lot) always have problems. I bet that is what you are observing.

:ok:

[RatsoreA]

As soon as I saw this thread go up, I thought, Jaba will be all over this very soon, and you did not disappoint!

I like my Contis for starting simplicity.... Prime it just shy of it catching fire and hit the switch and away she goes! :}

How much priming is just before catching fire? Well, that's the rub, isn't it!:E

[27/09]

Jabba:I would bet your local school 172's are not being started exactly as I describe. There will be all manner of throttle positions, mixture, priming and hence the problems.I have no doubt you're correct on that score. Plenty of fried starters and flat batteries. :{

Jabba:The engine, provided it has good plugs, good mags and a F/A ratio that is right, WILL start every time. No argument. The pilot controls the F/A ratio and assuming the engine is "conforming to spec" all you do is get the F/A ratio right.Agreed on having the F/A ratio correct.

I find with a hot start if it doesn't start after the first or second attempt you will need to prime. The amount of priming required can be hard to determine. On the next attempt after priming if there's not ignition after 4 to 5 blades I start opening the throttle to vary the F/A and almost always get a successful start.

Advancing the throttle on the first attempt at a hot start very often works as well.

[Adsie]

ACMS

True - but then push down gear lever down after RH engine has shut down to check LH engine hydraulic pump

But - [ and there is always a "but" ] when checking LH hyd. pump on shut down, it may be a bit lazier due to higher hydraulic oil temp

[Sunfish]

Rotax 912 iS….no mixture control so no argument;)

[Slippery_Pete]

What I do, for a conti semi-hot start on level ground, is...

1. Pat my head and rub my tummy
2. Flick the fuel pump on and off quickly five to seven times depending on the height of my shortest passenger
3. Say a short prayer
4. ....

Oh wait a minute, that's right. I don't any of those old wives tales and make up bull**** as I go along.

I just do what the AFM/AOM says on any type I fly - and LO AND BEHOLD.... it works every time.

Who'd have thought the AIRCRAFT MANUFACTURER would know the best way to start their aircraft, ey?

/End rant.

[Jabawocky]

Pete, that is good. But not all POH's are created equal.

We (APS) know and actually highlight in class, several POH's that are, lets call it sub-optimal in terms of reliable information. One that springs to mind is inflight restarts. Don't ask me which one off the top of my head, but lets just say the book describes a process that makes it worse not better. ;)

So the idea is understand the science, then you can critically think through the POH and determine if the one you are reading is a gem POH, or a POS.

Cheers :ok:

[Jabawocky]

27/09

That is about all there is to say about that! :ok:

[yr right]

gee wouldn't it be great if the manufactures provided a system that when running at or just above idle the engine actually took care of its on f/a mixture. perhaps they could call it lets say an idle circuit. omg what did you say they already do well ill be ???????

[PA39]

Yep Jabba...that's 100% correct. That's what I was trying to put across but went a little awry!...put it down to old age mate :(

[601]

I noticed that no one has mentioned the Lycoming IGSO-480s and Lycoming IGSO-540s.:cool:

[outofwhack]

Thanks Shytorque - I've been after a good explanation of this conundrum for years.

You land and then taxi to the ramp and cut the fuel to your hot fuel injected Lycoming by starving it of fuel by pulling the mixture.
Then as if by magic 5 mins later you start the engine with the mixture still cut off!

Heat soak! Simples

[flyinkiwi]

There's one flying school not far from here who's students seem to have no end of bother with hot starts on their injected C172's. However like anything YMMV.

Also I have a lot of experience with pilots new to an aircraft and or fuel injection and they tend to be ham fisted with starts usually having too much throttle set...

I've seen <insert name of nearby sausage factory> students in brand new 172's use the cold start procedure after refuelling and sit there wondering why it won't start. It's enough to make you weep. :ugh::mad::{

[Jabawocky]

I've seen <insert name of nearby sausage factory> students in brand new 172's use the cold start procedure after refuelling and sit there wondering why it won't start. It's enough to make you weep.

I have seen this at Parafield in Adelaide. The FCU's have to come off so often to get all the dye and goo cleaned off the diaphragm about every oil change! I kid you not.