Help Me With My Hot Start Technique (or Lack Thereof)

[bigmo]

Still getting used to my new-to-me 1970 M20F. I've read literally EVERY starting thread here - and might just be brain fried lol.

My cold starts are easy. For cold, I'm throttle at my gear clicker, full mixture, boost pump on for 8 Mississippi's, mixture off, boost pump off, pause for 8 Mississippi's - key and it lights on 1-4 blades. Easy peasy.

Hot...grrrr... Double grrr...

Tonight I did a quick turn gas with the engine at full operating temp. My stop was MAYBE 10 mins (more like 7-8). It was hot enough that the engine was still clicking and I could hear the fuel vaporizing and moving around in the lines. I thought - oh boy - this will be fun.

First, I tried the "don't touch a dang thing" method. Power was left at 1000rpm, did not touch the mixture. Just master on, clear and key. Nada. 20 blades and I called it quits. Did that one more time. 15 blades. No sign of life.

Second, I tried the previous owner's procedure (but he never did full hots - more like lunch, pee, gas, talk airplanes - call it 90-120 mins). His "hot start" was throttle at gear clicker, master on, mixture wide open (fast), blip boost pump for 1/4 sec, mixture off. Key. When I did that, I did get two little "almost starts" - where the engine gets ahead of the starter and feels like it's wanting to catch. When I fed it fuel, it just went back to cranking and no sign of life. I did this twice with the same result. So. Help critique. When the engine starts to catch (and I mean like not really running - but kind of running), do you feed it fuel or not? It did not seem to like fuel. I did not try a third where I did not move the mixture.

I did what works. Standard cold start. Know it's flooded. Open the throttle, mixture off. Crank. 10-15 blades, knick the boost pump, 10-15 blades, knick it again, and it'll catch. I HATE this process. I feel like I'm killing my starter and battery.

VERY open to some creative alternatives. It's getting to the point I am fearful of hot fuels and find myself avoiding them at all costs!

 

 

[1964-M20E]

When I shutdown for fuel like that I set the throttle 1200 to 1300 rpm then shut down.  Hopefully with the nose facing into the wind.  Also as I'm in the pattern I open the cowl flaps too get little extra cooling before shutdown.  After fueling or other activities and ready for the hot start I don't touch anything turn on the boost pump and turn the key to start.  Usually works good for me.

[KSMooniac]

Concur with the higher RPM setting... I idle at 1100 or 1200 and slowly pull the mixture back to ICO. Hot start with everything left where it was, no boost pump unless it starts stumbling after it catches.

If that fails, then flood it and use the flooded start procedure, but you need 3 hands to do that elegantly so I don't like to do it.

Weak ignition systems make starting more difficult too, so hopefully yours is in-spec.

Sent from my motorola edge plus 2023 using Tapatalk

[Ragsf15e]

+1 to ~1100 to 1200 idle.  No boost, no mixture. It should fire.  Is your ignition system solid?

If that doesn’t work, I might try a short prime, then crank it.  I say this because you were stopped for such a short time, maybe it didn’t fully cook off the fuel and drain into the cylinder.

If that doesn’t work, then yes youre flooded.  I very rarely do a flooded start, but when i do, I start with full throttle, mix ico.  As soon as it starts cranking, I slowly pull the throttle back. Typically it fires around midway back.

[PT20J]

There is no rote method that always works. Success depends on understanding what's going on. Gasoline will only combust over a fairly narrow range of fuel-air mixtures. The mixture control controls the amount of fuel and the throttle controls the amount of air admitted to the cylinders during starting. When cold, you are admitting a known amount of fuel by priming and the air is fixed by the throttle setting. When hot, the air is the same with the same throttle setting, but the fuel is variable. Why? 

When you first shut down, the fuel lines to the injector nozzles are full of fuel. The residual heat from the engine with no cooling airflow starts to boil the fuel out of the lines into the intake manifold. If you restart soon (say within a few minutes) this fuel "primes" the engine and it will start with the throttle cracked and the mixture in ICO. As soon as it starts, smoothly advancing the mixture to full rich will keep it running.

If it has been sitting longer, the fuel will have evaporated and the lines to the nozzles are dry and it won't want to start unless you crank long enough to fill the lines. If you prime as cold it will flood. But, often turning on the boost pump for a second or so will refill the lines enough to let it start without flooding. 

This all assumes that your ignition system is good: Timing correct, magnetos serviced within the last 500 hours, spark plugs clean and gapped properly.

The RSA fuel injection system does not meter fuel based on airflow below about 1200 rpm. So, to make it idle properly, the throttle is connected to an idle fuel valve by a linkage so that throttle position controls fuel flow at low rpm. The proper way to prime is to open the throttle at least 1/4 so that the fuel flow is not restricted. This should require about 4 seconds of prime. The reason you need twice that is because you have the throttle more closed. But, this introduces an additional variability in priming that may be an issue over a wider range of ambient temperatures and altitudes.

[Shadrach]

On 10/9/2024 at 9:09 PM, bigmo said:

Still getting used to my new-to-me 1970 M20F. I've read literally EVERY starting thread here - and might just be brain fried lol.

My cold starts are easy. For cold, I'm throttle at my gear clicker, full mixture, boost pump on for 8 Mississippi's, mixture off, boost pump off, pause for 8 Mississippi's - key and it lights on 1-4 blades. Easy peasy.

Hot...grrrr... Double grrr...

Tonight I did a quick turn gas with the engine at full operating temp. My stop was MAYBE 10 mins (more like 7-8). It was hot enough that the engine was still clicking and I could hear the fuel vaporizing and moving around in the lines. I thought - oh boy - this will be fun.

First, I tried the "don't touch a dang thing" method. Power was left at 1000rpm, did not touch the mixture. Just master on, clear and key. Nada. 20 blades and I called it quits. Did that one more time. 15 blades. No sign of life.

Second, I tried the previous owner's procedure (but he never did full hots - more like lunch, pee, gas, talk airplanes - call it 90-120 mins). His "hot start" was throttle at gear clicker, master on, mixture wide open (fast), blip boost pump for 1/4 sec, mixture off. Key. When I did that, I did get two little "almost starts" - where the engine gets ahead of the starter and feels like it's wanting to catch. When I fed it fuel, it just went back to cranking and no sign of life. I did this twice with the same result. So. Help critique. When the engine starts to catch (and I mean like not really running - but kind of running), do you feed it fuel or not? It did not seem to like fuel. I did not try a third where I did not move the mixture.

I did what works. Standard cold start. Know it's flooded. Open the throttle, mixture off. Crank. 10-15 blades, knick the boost pump, 10-15 blades, knick it again, and it'll catch. I HATE this process. I feel like I'm killing my starter and battery.

VERY open to some creative alternatives. It's getting to the point I am fearful of hot fuels and find myself avoiding them at all costs!

 

 

An unprimed IO360 should start in 20 blades whether hot or cold. Given that yours does not, I would suspect something else is going on. 20 blades after a 10 minute stop makes zero  sense.  I flew my aircraft to North Carolina early this week to support disaster relief, repositioning on the field three different times before departing. Times between startup buried between 10 minutes and 30 minutes.. The airplane started every time without prime
I have been flying this engine for more than 20 years and the only time I’ve had the kind of symptoms you describe are when there’s an ignition problem. 
 

@PT20J Skip gives good advice and information above.
What is a “gear clicker“ and what does that mean in terms of throttle position? An eight Mississippi prime is an awful lot. If I primed that long on a normal cold start, I would surely hear a bang from the exhaust when the engine fired. I use a four second count with throttle open. I might do closer to eight seconds if it’s freezing or below, but I’d probably try six first.

[Joshua Blackh4t]

Ditto all the above advice.

Don't be scared to open the throttle way more on a hot start. 3/4 inch is a good place to start. 

If it has only been minutes (quick refuel) and doesn't fire, try full throttle.

If its been over an hour, or if the above doesn't work, a split second of priming and 3/4 inch throttle.

 

The one that gets me is if it catches an I open the mixture and it dies. Did I flood it or is it starving?

I'm trying to train myself to open it slower when hot. That way if it dies then its starved, I can prime it and we're good. 

Yes, its frustrating, and still gives me anxiety. But you do get better at it.

Also remember it changes with temperature as well. Strangely enough, hot temps seem to flood quicker

 

[N201MKTurbo]

My hot start technique has been the same with both my Mooneys and has always worked. Set the throttle to about 1000 RPM, your clicker should work. Mixture to ICO. Crank till it fires then wait till it starts to die then advance the mixture. 
 

Always assume it is flooded. It never needs a prime when hot.

If the above technique fails, then flood the engine with the pump and do a flooded start.

[Shadrach]

2 hours ago, Joshua Blackh4t said:

Ditto all the above advice.

Don't be scared to open the throttle way more on a hot start. 3/4 inch is a good place to start. 

If it has only been minutes (quick refuel) and doesn't fire, try full throttle.

If its been over an hour, or if the above doesn't work, a split second of priming and 3/4 inch throttle.

 

The one that gets me is if it catches an I open the mixture and it dies. Did I flood it or is it starving?

I'm trying to train myself to open it slower when hot. That way if it dies then its starved, I can prime it and we're good. 

Yes, its frustrating, and still gives me anxiety. But you do get better at it.

Also remember it changes with temperature as well. Strangely enough, hot temps seem to flood quicker

 

When it fires and dies, It’s almost always lack of fuel from not advancing the mixture in a timely manner. A properly set up IO360 fuel system won’t flood a running engine with a full rich mixture unless you’re at high DA. 
 

If you miss the first time it catches on a hot start, give it one thousand one, two, shot of prime with the throttle cracked. It should fire off again easily. If you miss it again, do it again. The IO360s reputation for difficult hot starts far exceeds. It’s operational reality. I have zero anxiety about starting my Aircraft under any conditions. There is no reason why others shouldn’t be the same.

[bigmo]

Thanks all for the great feedback. Looks like lots of ways to skin cats here. I think my goal over the next couple of weeks is to fly daily for an hour, come back to the hangar, pause for 10 mins simulating my fueling, and then try one each day a "new technique" - and find one that seems that the aircraft likes best.

I called a local mechanic that's a local Mooney expert. He explained to me that when you shut down, the engine is flooded - period. He spent some time talking about the way the FI meters fuel (similar to @PT20J described). His advice was mixture cutoff, full throttle, crank and don't be anxious to cram the mixture in.

I'll give that a whirl first.

If that's unsuccessful, my next experiment will be @1964-M20E method - I have a hunch my a/c might like this approach.

I'll keep working through techniques until I find a winner (in a stress free environment). 

 

 

[Shadrach]

30 minutes ago, bigmo said:

I called a local mechanic that's a local Mooney expert. He explained to me that when you shut down, the engine is flooded - period. He spent some time talking about the way the FI meters fuel (similar to @PT20J described). His advice was mixture cutoff, full throttle, crank and don't be anxious to cram the mixture in.

I don’t like to be a nitpicker, but I must disagree with the assertion that an IO360 floods when shut down. It does not. Skip already did an excellent job of explaining what happens to the fuel in the lines  at shut down. This is not a flooded condition. If it were, the engine would not fire off in 5 to 8 blades with the throttle set for 1000 RPM, which is the norm. 
 

Here’s the bottom line. When you start an IO360 within an hour of shut down, there should be adequate fuel in the manifold to support start up without priming. If it fails to start, the best course of action is to add fuel (prime) in very small quantities. Leave the throttle alone.

FYI, when you flood an engine, it is entirely possible to end up on fire. I have seen it happen on two occasions at the fuel farm

[Slick Nick]

Another thing I noticed from watching youtube videos, is people tend to "shove" the mixture full in as soon as the engine catches. Move it SLOWLY, think 3-4 seconds to reach full rich. There's no rush. Shoving it in causes the engine to stumble, and then it revs to the moon once it clears itself out. Not what you want to do on an engine before it builds oil pressure.

[Slick Nick]

5 hours ago, Shadrach said:

What is a “gear clicker“ and what does that mean in terms of throttle position? An eight Mississippi prime is an awful lot. If I primed that long on a normal cold start, I would surely hear a bang from the exhaust when the engine fired. I use a four second count with throttle open. I might do closer to eight seconds if it’s freezing or below, but I’d probably try six first.

I think he's referring to the gear warning horn switch. You can hear / feel a click as the throttle is advanced past about a quarter inch. 8 seconds is an eternity, so is 4 for that matter. The POH says to only run the pump long enough to "establish fuel pressure" which is about 2-3 seconds at the most.

[bigmo]

22 minutes ago, Slick Nick said:

I think he's referring to the gear warning horn switch. You can hear / feel a click as the throttle is advanced past about a quarter inch. 8 seconds is an eternity, so is 4 for that matter. The POH says to only run the pump long enough to "establish fuel pressure" which is about 2-3 seconds at the most.

Yes, that's the gear clicker I was referencing.

My F takes 4 secs for the fuel pressure to stabilize at 25psi. I was giving it 4 secs past pressure built, but will reduce that to 2 and even 1 and try those options. 

That said, my cold starts are 1-4 blade events.

[N201MKTurbo]

It's not how fast you add the mixture, it is when you add mixture, your timing needs to be precise, A smooth steady advance is best.

[EricJ]

2 hours ago, Shadrach said:

A properly set up IO360 fuel system won’t flood a running engine with a full rich mixture unless you’re at high DA. 

The only time I've had much trouble with a hot start was at high DA on a hot day.    Took forever, but did finally start and stay running.

Otherwise the usual advice in the thread applies.   After a while it gets pretty routine.

[Will.iam]

Poor guy at the fuel pump after filling up gave a shot of primer and then tried to start engine would fire on one or 2 cylinders then quit he would then repeat the process with the exact same thing happening. This went on for 8 or 9 tries. I finally went over there and said skip the priming you are too rich. Next try the engine started to fire on one then 2 then finally 3 and 4 started firing tones of black smoke out the exhaust pipe as the engine slowly cleared itself. If after 2 tries keep the mixture closed and no boost open up the throttle and crank I. E. Try to clear the flooded engine if it starts and dies at least you now know it’s not flooded and can go from there. This guy just keep his engine so flooded it was never going to run. 

[N204TA]

My hot start procedure for my’68 F is this:

1.  Mixture full rich

2.  Full Throttle 

3. Mixture idle-cutoff

4.  Master On

5.  Engage starter

6.  When the engine catches, reduce throttle with one hand and slowly increase the mixture with the other.  It takes a few seconds of finesse to get the perfect combination of throttle and mixture to get the engine running smoothly then I pull the throttle to idle and set the mixture as needed.

[bigmo]

10 minutes ago, N204TA said:

My hot start procedure for my’68 F is this:

1.  Mixture full rich

2.  Full Throttle 

3. Mixture idle-cutoff

4.  Master On

5.  Engage starter

6.  When the engine catches, reduce throttle with one hand and slowly increase the mixture with the other.  It takes a few seconds of finesse to get the perfect combination of throttle and mixture to get the engine running smoothly then I pull the throttle to idle and set the mixture as needed.

Interesting. No pump right? And how long do you leave the mixture at full rich?

This will make my "trial list".

[N204TA]

19 minutes ago, bigmo said:

Interesting. No pump right? And how long do you leave the mixture at full rich?

This will make my "trial list".

No pump on a hot start, correct.  I only leave the mixture full rich for just a couple of seconds…usually not much longer than it takes to move the throttle to full.  My theory is that it helps break any vapor lock as I usually see the fuel pressure gauge fluctuate as I bring the throttle in and the mixture out.

[Shadrach]

52 minutes ago, N204TA said:

My hot start procedure for my’68 F is this:

1.  Mixture full rich

2.  Full Throttle 

3. Mixture idle-cutoff

4.  Master On

5.  Engage starter

6.  When the engine catches, reduce throttle with one hand and slowly increase the mixture with the other.  It takes a few seconds of finesse to get the perfect combination of throttle and mixture to get the engine running smoothly then I pull the throttle to idle and set the mixture as needed.

You could simplify things by eliminating step 1, 2 and 3…

[bigmo]

16 minutes ago, Shadrach said:

You could simplify things by eliminating step 1, 2 and 3…

I do sincerely appreciate everyone's feedback. But the "don't touch anything" method did not work for me. It's why I'm gathering as much info as I can so I can see what works for my plane. @N204TA process is close to what my source (and this guy DOES know his stuff) said to try. 

I do find it interesting that MS tends to really follow Mooney factory guidance on just about everything BUT starting. The Mooney cold and hot starting procedures are literally never recommended. About the only logic I find in the POH is their hot start procedure will surely flood it, so it's ALMOST like they want you to just flood it and move to flooded start.

I will have the mag timing checked and can pull and check plugs, but the plane is 20 hours out of annual and has < 100 hours on the mags. Starter & battery both good.

 

[N204TA]

4 minutes ago, bigmo said:

I@N204TA process is close to what my source (and this guy DOES know his stuff) said to try. 

 

 

It’s worked for me for 30 years and over 3,000 hours.

[Shadrach]

20 minutes ago, bigmo said:

I do sincerely appreciate everyone's feedback. But the "don't touch anything" method did not work for me. It's why I'm gathering as much info as I can so I can see what works for my plane. @N204TA process is close to what my source (and this guy DOES know his stuff) said to try. 

I do find it interesting that MS tends to really follow Mooney factory guidance on just about everything BUT starting. The Mooney cold and hot starting procedures are literally never recommended. About the only logic I find in the POH is their hot start procedure will surely flood it, so it's ALMOST like they want you to just flood it and move to flooded start.

I will have the mag timing checked and can pull and check plugs, but the plane is 20 hours out of annual and has < 100 hours on the mags. Starter & battery both good.

 

If the engine is running well, I would focus on ensuring that the left mag is firing at TDC.

[A64Pilot]

In my experience most of the time as in way more often than not a difficult to start engine that was recently shut down is from a weak ignition system, very often as in more often than not it’s as simple as carboned up plugs. 

Especially if it used to start but has been getting harder and harder requiring more finesse in the technique.

Edited October 10 by A64Pilot