NEW Cold Start anomaly

[Echo]

The last tenish cold starts of my plane have been different.  Instead of firing off the engine sputters and hitches pretty violently before smoothing out.  I leave throttle at 1200 on shutdown.  I prime for a count of five.  Mixture rich on starting.  Thoughts?

About 500 hours on a MFRER new limits engine.  Six years since major.

[47U]

49 minutes ago, Echo said:

Thoughts?

Does your engine monitor identify which cylinder(s) are not participating?  Sounds like one or more sticking exhaust valves, aka, morning sickness.

Smart people will be along shortly… I’ve not finished my morning coffee so not fully awake.

[DCarlton]

I get a strong 2-3 sec shutter occasionally too.  I long ago put that in the normal category.  I think I've gotten it starting and shutting down.  Interested in hearing what the mechanics say.  I've always thought it was remarkable that the cowl and engines mounts stay screwed together and undamaged as well as it does.  If only the accordion intake boot didn't wear out eventually.  Will the engine monitor indicate anything during the first few seconds of engine start?  I've never considered looking.  Hum... 

[bonal]

Hey Scott, I know mine is a o360 and not the same but every time I do the first start of the day it fires instantly but it’s a very sudden almost like a bang and then perfectly smooth. It’s not a backfire like a jolt kind of hard to describe but it’s always done this.  When I crank it I don’t even see two blades before it starts.  I don’t know if that’s what you’re describing but kind of sounds the same.  Might be nothing.  
 

I re read your description and see where you have sputtering first so that would be different than what I experience except for violent part.  Could be the difference between a carburetor prime and an FI one.

Edited 13 hours ago by bonal

[MikeOH]

Has the OAT been different for the last ten starts vs. previously?

I've experienced what you have when I have OVER primed.  I do NOT ever go full rich when starting; I'm at ICO after priming, crank and as the engine fires I slowly advance the mixture until the engine runs smooth.  Then reduce the mixture after a minute or so when there is engine temp rise.

[Echo]

16 minutes ago, MikeOH said:

Has the OAT been different for the last ten starts vs. previously?

I've experienced what you have when I have OVER primed.  I do NOT ever go full rich when starting; I'm at ICO after priming, crank and as the engine fires I slowly advance the mixture until the engine runs smooth.  Then reduce the mixture after a minute or so when there is engine temp rise.

Thanks to everyone for replies.  Mike I will try less prime.  I have always done a five count through just under 1000 hours and first plane did NOT have this issue.  This plane now has a SkyTech and STILL is a cranky hard starter.  My cold start process is identical to yours except perhaps prime duration?  The engine is a complete shit show for five seconds after starting...Then smooths out like a purring kitten.  I have no idea what is up, but it is the same every time...rough running and threatening to quit and LOTS of vibration.  A lot of drama...It has champion massives...that I hate.  I am going to replace plugs with Tempest massives and see what happens.

[MikeOH]

@Echo

FWIW, I have had good luck with a 3 count for prime. Granted I'm in southern California and I'm normally starting with OAT between 65 and 80 most of the time.  If it's hotter than 80-85 I'll just prime a second or two. Colder than 55 and I'll go closer to 5 seconds.  I don't think I've ever started at less than 50 

Oh, and I wait at least 5 seconds (when it's >75), and longer if colder after priming and before I crank.

[Vance Harral]

The "takes a few seconds to settle down" occurs in our IO-360-powered M20F as well.  It's been doing that for literally two decades, and I've come to think of it as normal.  But it still bugs me because it would make it difficult to distinguish actual morning sickness (stuck valve) from whatever is otherwise happening.

That said, you're wise to note that this is a new behavior.  Something has changed.  It might be a change in the starting mixture based on a change in air density relative to your constant 5 seconds of prime.  But I'm always a little skeptical about this stuff.  Pilots tend to claim there are known good formulas for priming, e.g. "5 seconds when cold, 3 seconds when warm" or whatever.  But I think the actual fuel/air mixture you get in the cylinders at engine start is a result of multiple complex inputs (not just air temperature, but also fuel servo temperature, throttle position, rate at which you move the mixture lever, and so on); and that an engine that starts easily mostly does so through the grace of there being a broad variety of fuel/air mixtures that are combustible.

[MikeOH]

6 minutes ago, Vance Harral said:

Pilots tend to claim there are known good formulas for priming, e.g. "5 seconds when cold, 3 seconds when warm" or whatever.  But I think the actual fuel/air mixture you get in the cylinders at engine start is a result of multiple complex inputs (not just air temperature, but also fuel servo temperature, throttle position, rate at which you move the mixture lever, and so on); and that an engine that starts easily mostly does so through the grace of there being a broad variety of fuel/air mixtures that are combustible.

I think you nailed it.  I, in no way, claim my 5 or 3 or whatever seconds is a 'formula'.  I think it just improves the ODDS that you end up in that 'range of fuel/air mixtures that are combustible'.  There are, as you say, way too many variables at work on any given start.

[Hank]

Threads like this make me thankful for the forgiving carburetor in my O-360, especially with winter and real cold starts approaching . . . Even if many of you think that 'Bama cold isn't real cold . . .

• Electric pump on until fuel pressure stabilizes, then off.
• Mixture rich
• Pump throttle (twice in warm weather, up to 5 times when below freezing), leave ~1/4" forward (fuel pressure should drop slightly on each pump, and stabilize)
• Wind and set clock (and wait a bit longer when below freezing--put on and adjust headset) to allow the fuel in the carb to vaporize.
• Turn key and push, release when engine fires and catches
• Set throttle for 1000 RPM

It seems as if every E, F & J pilot has their own secret recipe for hot starts, and now the secrets are coming out for cold starts, too. For my own hot starts, I just omit running the fuel pump and pump the throttle twice regardless of OAT, and shorten up the waiting.

Hope you get it figured out!

[MikeOH]

It also helps that I just won’t go outside if it’s below freezing 

[Vance Harral]

1 hour ago, Hank said:

Pump throttle (twice in warm weather, up to 5 times when below freezing)

@Hank probably knows this, but just for others reading the thread... some carbureted aircraft don't have a primer systems that inject fuel directly into the cylinders.  Including some Mooneys, and I'm guessing Hank's is one of them.  Pumping the throttle to force the accelerator pump to spray atomized fuel up into the carburetor throat is the only way to prime the engine in these airplanes.  But please be careful about dispensing "pump the throttle to prime" advice, even in carbureted aircraft.  Most carbureted airplanes have updraft carbs (fuel/air path into the engine intake is opposite gravity), and some of them don't atomize the fuel all that well, especially when it's cold.  In these aircraft, some of the fuel you shoot into the carburetor throat by pumping the throttle runs back down over the carburetor, into the engine cowl, onto the ground, etc.  This is a fire hazard, and not just a theoretical one - a 182 at our flight school suffered significant damage in a carburetor fire caused by someone who wasn't very skilled getting the engine started, and managed to light off an engine compartment fire after excessive throttle pumping.  It's definitely safer to use a primer vs. pumping the throttle, though the risk reduction is hard to quantify.

If you must pump the throttle to get the engine started, one way to mitigate risk is to only pump the throttle while actually cranking the starter.  With this method, the vacuum generated in the intake by the moving cylinders will draw more of the fuel droplets up into the engine, less of them will rain down on the ground.  I'm aware this isn't the POH procedure, but it has been effective for me in a number of carbureted airplanes, and I think it's safer.

1 hour ago, Hank said:

For my own hot starts, I just omit running the fuel pump and pump the throttle twice regardless of OAT, and shorten up the waiting.

The "hot start problem" in fuel injected engines is almost entirely caused by the the fuel injector lines being routed right over the cylinder heads, such that the fuel in them is baked and vaporized by the hot cylinders as soon as cooling air stops flowing over them, i.e. immediately after shutdown.  Lycoming/Continental carbureted engines don't have this problem because the entire fuel/air intake system is below the hot cylinder heads, so there's really no comparison between carbuerted/fuel-injected with regard to hot starts.  Indeed, carbureted engines are almost always blissfully easy to start when warm.

For what it's worth, your engine would likely start with zero throttle pumps when warm, albeit after a few more blades than with pumping.  Reduces the admittedly small risk of a carburetor fire, at the expense of more wear on your starter.

[Hank]

@Vance Harral, I'm not aware of ANY carbureted Mooneys with separate primer functions like found on the 172s I trained in. 

When cranking in very cold weather, I sometimes also pump the throttle a few times as the engine turns over, especially if it fires unsuccessfully a couple of times.

Unless the engine is flooded, there is little risk of an engine fire.

At the risk of derailing discussion here, this is from my Owners Manual:

[Echo]

No worries Hank (on derailing).  I am going to try and prove I am not crazy (doing same thing over and over and expecting different result) and try less boost pump.  (opposite of more cow bell if you are a Blue Oyster Cult/SNL fan).

[carusoam]

17 minutes ago, Echo said:

No worries Hank (on derailing).  I am going to try and prove I am not crazy (doing same thing over and over and expecting different result) and try less boost pump.  (opposite of more cow bell if you are a Blue Oyster Cult/SNL fan).

One thing for sure…

if you have learned to use a certain amount of prime in warm weather…

and the temps have cooled a bit…

less prime won’t make any sense (to a chemical engineer).

100LL is known for its inability to evaporate as temps cool…

the IO550 uses 40°F as the cut-off from normal start to cold start… where additional seconds of prime are used… and running the fuel pump on Lo to keep it running for a few more seconds…

read up on various starts to understand them better… as a flooded start may be in your future…

Best regards,

-a-

[N201MKTurbo]

I always start IO-360s the same no matter what the temperature. It never fails. Mixture rich, throttle at ~1000 RPM setting. Crank the starter, if it isn’t making fuel pressure, I’ll turn on the boost pump until I have fuel pressure, then turn it off. 
 

The only time I prime is if I think it is flooded, I will prime to make sure it is flooded, then do a flooded start.

Hot start is mixture ICO, throttle 1000 RPM, crank till it starts, then advance the mixture.

Flooded start is the same as hot start, but with more throttle. When it finally catches, reduce the throttle and when it starts to die, advance the mixture.

[Echo]

4 minutes ago, N201MKTurbo said:

I always start IO-360s the same no matter what the temperature. It never fails. Mixture rich, throttle at ~1000 RPM setting. Crank the starter, if it isn’t making fuel pressure, I’ll turn on the boost pump until I have fuel pressure, then turn it off. 
 

The only time I prime is if I think it is flooded, I will prime to make sure it is flooded, then do a flooded start.

Hot start is mixture ICO, throttle 1000 RPM, crank till it starts, then advance the mixture.

Flooded start is the same as hot start, but with more throttle. When it finally catches, reduce the throttle and when it starts to die, advance the mixture.

Well, THAT is a new one. Start cranking with full rich on a cold engine.

[N201MKTurbo]

If you prime an IO-360, you will fill one cylinder with fuel, maybe. The rest just goes into the sump. If the sump is cold, it will just sit there or drain out the sniffle valve. 
 

Once you have fuel pressure, the injectors will provide a perfect mixture for starting. Why mess with it.

[N201MKTurbo]

2 minutes ago, Echo said:

Well, THAT is a new one. Start cranking with full rich on a cold engine.

I’ve started them in zero degree F weather like that.

[N201MKTurbo]

49 minutes ago, Hank said:

@Vance Harral, I'm not aware of ANY carbureted Mooneys with separate primer functions like found on the 172s I trained in. 

When cranking in very cold weather, I sometimes also pump the throttle a few times as the engine turns over, especially if it fires unsuccessfully a couple of times.

Unless the engine is flooded, there is little risk of an engine fire.

At the risk of derailing discussion here, this is from my Owners Manual:

You know the O-360 and IO-360 are very different to start. 

[Hank]

6 minutes ago, N201MKTurbo said:

You know the O-360 and IO-360 are very different to start. 

Yep. I knew hot starts were very different; this thread points out that ALL starts are very different between the O- and the IO engines!

[PT20J]

If you overprime an IO-360, it runs a little rough for a few seconds after starting. But if it is REALLY rough then it’s more likely a sticking valve. If you have an engine monitor, it’s easy to see which cylinder is dead because the EGT won’t come up. If you don’t have an engine monitor, start it with the cowling off an then shut down and feel which cylinder is cold.

[Echo]

1 hour ago, PT20J said:

If you overprime an IO-360, it runs a little rough for a few seconds after starting. But if it is REALLY rough then it’s more likely a sticking valve. If you have an engine monitor, it’s easy to see which cylinder is dead because the EGT won’t come up. If you don’t have an engine monitor, start it with the cowling off an then shut down and feel which cylinder is cold.

Not a valve issue.  Thanks for input.  I have an edm830.  I looked.

[47U]

5 hours ago, Echo said:

(opposite of more cow bell if you are a Blue Oyster Cult/SNL fan).

Or, LESS DOORBELL!

We had a pilot at Beale, ‘Mango’.  His Christopher Walken impression was spot-on.  ‘More cow bell’ was a running joke in the office.