M20C Cold Weather Start

[MoonMan]

I recently had trouble starting my M20C while on a trip. I had left it tied down on the ramp, and overnight lows were around 35 degrees.  In warm weather (say 50 degrees or warmer) I’ve always turned on the boost pump, pumped the throttle twice, and it fires within a couple of blades. During this start, I pumped the throttle three times, and cranked for a few seconds, and it didn’t fire. I gave it a couple more pumps, cranked again, and nothing. I got out to check to see if I had flooded it, but didn’t see or smell any fuel. On the third try, after another three pumps of the throttle it started.

What is everyone’s procedure for starting an M20C with no primer in the colder weather? My plane is usually hangared (in NC) and overnight the hangar rarely gets below the upper 40’s, (and I use a Twin Hornet heater with some heavy blankets over the cowl when it does).  I saw a video on YouTube where the guy pumps the throttle 10 times before starting in cold weather. This seems excessive, and a possible fire hazard. Also, do you leave the boost pump on while cranking?  I would like a better starting procedure for the next time I’m faced with the same conditions. Thanks. 

[Ragsf15e]

18 minutes ago, MoonMan said:

I recently had trouble starting my M20C while on a trip. I had left it tied down on the ramp, and overnight lows were around 35 degrees.  In warm weather (say 50 degrees or warmer) I’ve always turned on the boost pump, pumped the throttle twice, and it fires within a couple of blades. During this start, I pumped the throttle three times, and cranked for a few seconds, and it didn’t fire. I gave it a couple more pumps, cranked again, and nothing. I got out to check to see if I had flooded it, but didn’t see or smell any fuel. On the third try, after another three pumps of the throttle it started.

What is everyone’s procedure for starting an M20C with no primer in the colder weather? My plane is usually hangared (in NC) and overnight the hangar rarely gets below the upper 40’s, (and I use a Twin Hornet heater with some heavy blankets over the cowl when it does).  I saw a video on YouTube where the guy pumps the throttle 10 times before starting in cold weather. This seems excessive, and a possible fire hazard. Also, do you leave the boost pump on while cranking?  I would like a better starting procedure for the next time I’m faced with the same conditions. Thanks. 

You’ll get some help soon from an actual C owner, but the cold weather makes it a lot harder for the fuel to vaporize.  They generally all need more prime when it’s cold, so it seems that you probably just need a little better “cold start” technique.  I have fuel injection, so can’t help, but the C guys will be along as this is pretty common.

[Ragsf15e]

@Skates97 or @Hank or @Utah20Gflyer can probably help.

[PT20J]

I think you answered your own question: you primed more (using the throttle accelerator pump) and it started. So it just needs more prime when it’s cold.  It’s got a float carburetor, so the electric fuel pump shouldn’t make a difference. If you pump the throttle while cranking, the fuel will be sucked into the intake pipes and won’t pool which is what creates the fire hazard. 

[Bartman]

My fuel injected engine requires 3 seconds of prime and wait a few seconds before cranking in the summer. In the winter she requires 5-6 seconds of prime, but the most important thing is to wait about 20 seconds to allow fuel to vaporize before cranking.

I don’t know about priming with a carb and no prime pump, but allowing time for the fuel to vaporize is essential for my cold weather starts. 

[N201MKTurbo]

Sometimes hen it is real cold, moisture will flash freeze on the plugs and short them out. The heat of compression will often heat the cylinders from cranking. If it just refuses to start, wait about 5 minutes and try again. Besides, the initial cranking will heat the battery, so waiting will also let the heat in the battery work its way through the battery and it will crank harder the second time.

[C.J.]

@MoonMan 

I prime with 6 throttle pumps with boost on below 50*F (4 throttle pumps when above 50*F) then boost goes OFF.

Throttle cracked 1/4 - 1/2 inch 

Wait :30 seconds for fuel to atomize and then engage starter. My engine always starts in 2 seconds (yes, I've timed it)

I don't pump the throttle during the start.

I use a battery-minder charger/desulfator - battery is usually at 12.7 volts prior to start. 

[Hank]

I have an oil pan heater on my C that I like to use when it's going to be cold, for at least an hour. Sometimes this is not possible away from home (like on a large ramp).

My process is similar to @C.J.'s above, with a slight twist. It worked well-for me living in West-by-Gawd Virginny, and now in Sweet Home:

• Pull the prop through 2-3 revolutions before getting in (verify key not in ignition!)
• Master On
• Fuel Pump On until fuel pressure peaks and stabilizes (at top of green arc)
• Fuel Pump Off
• Mixture Rich
• Pump throttle 5-8 times (Fuel Pressure will drop a bit with each pump)
• Set ~1/4" throttle travel
• Wind and Set yoke clock and red hand pair
• Put on and adjust headset

(this gives the cold fuel time to vaporize)

• Turn the key and push
• If it fires but doesn't catch, pump the throttle a couple or three more times while continuing to crank
• Release key when running
• Lean mixture ~2/3 towards Idle Cutoff

If it's really cold, it may take two times doing this, but with decent preheat it's one-and-done.

Hope this helps!

[Ragsf15e]

9 minutes ago, Hank said:

I have an oil pan heater on my C that I like to use when it's going to be cold, for at least an hour. Sometimes this is not possible away from home (like on a large ramp).

My process is similar to @C.J.'s above, with a slight twist. It worked well-for me living in West-by-Gawd Virginny, and now in Sweet Home:

• Pull the prop through 2-3 revolutions before getting in (verify key not in ignition!)
• Master On
• Fuel Pump On until fuel pressure peaks and stabilizes (at top of green arc)
• Fuel Pump Off
• Mixture Rich
• Pump throttle 5-8 times (Fuel Pressure will drop a bit with each pump)
• Set ~1/4" throttle travel
• Wind and Set yoke clock and red hand pair
• Put on and adjust headset

(this gives the cold fuel time to vaporize)

• Turn the key and push
• If it fires but doesn't catch, pump the throttle a couple or three more times while continuing to crank
• Release key when running
• Lean mixture ~2/3 towards Idle Cutoff

If it's really cold, it may take two times doing this, but with decent preheat it's one-and-done.

Hope this helps!

This is getting more complicated than hot starting an IO-360?! 

[Hank]

47 minutes ago, Ragsf15e said:

This is getting more complicated than hot starting an IO-360?! 

Nah. The only things different from a normal start is pulling the prop through, additional throttle pumps and the pause before turning the key.

Doesn't your Owners Manual / POH have Cold Start instructions?

[PT20J]

These engines are all a little different. When I volunteered at the museum, we had a DC-3 with two identical P&W R-1830 engines. The left one always started right up. The right one seemed to depend on how you held your tongue. We spend a lot of time checking things and taking things to pieces and checking them and nothing seemed to change this.

But, the basic principle is always the same. If you have rotation and spark, it's all about getting a combustible fuel and air mixture into the cylinders. Best to start a little lean and add fuel until it lights off. The worst situation is to not know whether it is flooded or doesn't have enough fuel. That's how people run the battery down going from normal start to flooded start and back and forth until the battery is dead. If you get confused about whether it is flooded or not there are only two solutions. Let it sit for half an hour so that excess fuel has evaporated and start over, or, if you are in a hurry, make sure it is flooded (but not so much that you have a big puddle of fuel on the ground) and use the flooded start procedure.

[varlajo]

9 minutes ago, PT20J said:

The worst situation is to not know whether it is flooded or doesn't have enough fuel. 

Some in my corner of the woods swear by the "all starts are hot and flooded starts" philosophy, which appears to work well for them. Throttle full forward, mixture ICO, start cranking, move throttle to normal start position over 3 seconds, advance mixture to normal start position over another 3 seconds. If no start, turn on electric fuel pump while cranking. The first half of the procedure takes care of the first part of the uncertainty, and the second of the second. 

[47U]

6 hours ago, MoonMan said:

I saw a video on YouTube where the guy pumps the throttle 10 times before starting in cold weather. This seems excessive, and a possible fire hazard.

Make sure you have the hose that sticks out of the hole in the bottom of the cowling connected to the tube on the bottom of the air box.  Any excess fuel will drain to the ramp and not pool inside the lower cowl.

I think back to starting carburetor equipped cars back in the 60s and 70s when it’s really cold, below zero even.  If you’re cranking and it’s trying to run, it’s ok to pump the gas pedal (throttle) for more gas, which in the airplane will be sucked up into the intake.

[Fly Boomer]

11 hours ago, MoonMan said:

I recently had trouble starting my M20C while on a trip.

I don’t have a carburetor, but I read once (Mike Busch?) that if it won’t start and it’s hot, you probably over-primed, and if it’s cold you probably under-primed.

[Hank]

1 hour ago, Fly Boomer said:

I don’t have a carburetor, but I read once (Mike Busch?) that if it won’t start and it’s hot, you probably over-primed, and if it’s cold you probably under-primed.

Sadly, our planes don't have a primer. Just like my old pickup in college, in winter stomp on the gas pedal a few times before turning the key. Or in my Mooney, pump the throttle a few times; the colder the temps, the more times.

[midlifeflyer]

18 minutes ago, Hank said:

Sadly, our planes don't have a primer. Just like my old pickup in college, in winter stomp on the gas pedal a few times before turning the key. Or in my Mooney, pump the throttle a few times; the colder the temps, the more times.

I think the 20C has an accelerator pump, shooting fuel into the system, just like your old pickup. Is that correct, Hank?

[Hank]

8 minutes ago, midlifeflyer said:

I think the 20C has an accelerator pump, shooting fuel into the system, just like your old pickup. Is that correct, Hank?

That's right. See the Starting procedure i posted above.

[bcg]

I think you've already gotten some good feedback.  With my C, if it's below 40 and I can't plug in the oil pan warmer for an hour or more, I will turn the boost pump on and pump the throttle 6 - 8 times with mixture at full rich.  Then leave the throttle about 1/4 open and start cranking, advancing throttle slightly as it starts to catch, then pulling back to an idle and adjusting mixture once it's running. It took me a little while to figure out exactly what it wanted in cold weather, the first year I had it we had a lot of early mornings in the 20s and if I didn't plug the heater in, I couldn't get it started.  Since doing this, it usually kicks off within a few seconds. 

 

[Utah20Gflyer]

My cold weather start procedure

1.  Master on

2. Fuel pump on

3. verify fuel pressure 

4. mixture full reach 

5. pump throttle 5 times

6. Fuel pump off

7.  Wait 1 minute

8. Fuel pump on 

9. verify fuel pressure

10. throttle 1/4 inch in

11.  Crank engine

Waiting the one minute makes a big difference on my plane.  Most of the time if I botch a start it happens to be when I am impatient and don’t wait to crank.    After switching to a light weight/high speed starter my starts got easier.  
 

Only difference for a normal temp start is two pumps of the throttle and wait 30 seconds.   
 

If I were on a trip I would start at 35 degrees without a preheat, but when I’m at home I preheat below 45 degrees.  It makes the starts a non issue.  I really like getting a start on the second blade.  

[Vance Harral]

One thing I don't yet see mentioned in this thread is detail on exactly how to pump the throttle when using the pump-to-prime trick.  It matters.

As others have explained, throttle pumping is only meaningful in carbureted engines, whose carburetor is equipped with an accelerator pump.  I'll gloss over the details of exactly how an accelerator pump works, but the basic idea is to introduce an extra jet of atomized fuel into the intake when the throttle linkage is moved rapidly from low to high.  This prevents hesitation under rapid acceleration, and is the primary reason for having the accelerator pump.  The fact you can spray this extra jet of fuel into the intake before engine start as a priming mechanism is a secondary feature of the accelerator pump.

How much fuel is introduced by a pump of the throttle, and how well atomized the fuel spray is, depends on how rapidly the throttle linkage is moved.  A robust, rapid pump introduces a large, well-atomized dose of fuel into the manifold, while a slow pump introduces a smaller, less-well-atomized dose.  This variation increases as the components of the accelerator pump wear over time.

In practice, this means that advice to use some X number of pumps doesn't necessarily translate from one pilot to another, or one airframe to another, even when equipped with the same engine and carburetor.  More importantly, "slow" throttle pumping on a less-than-new carburetor often introduces little or no additional fuel at all.  And because lots of pilots have been taught to be smooth and deliberate with the engine controls, they are also slow and deliberate with throttle pumping, such that it works poorly or not at all.

Honestly, if you're performing effective throttle pumping to get the engine started, it should look vaguely obscene.   Because I am old and no longer easily embarrassed, I am willing to, uh... "vigorously" pump the throttle of a carbureted engine while cranking, and this has often allowed me to get a carbureted engine started on a cold morning when other pilots are unsuccessful.  You should be aiming for 2-3 full-stroke pumps per second, not one weak stroke every couple of seconds.  Insert your own joke here, but you get the idea.

[Hank]

Fast pumps are easier with my throttle quadrant compared to push-pull controls. 

[bonal]

I remember many years ago I used to work at a performance shop that did tire and wheel upgrades and we had contracts with a couple of the local Ferrari dealers.  I had the enviable job of picking up and delivering the cars in for modification.  Anyway after we finished the job and to be honest I can’t remember which model Ferrari it was I couldn’t get it to start.  While making another attempt my co worker came out and shouted they  converted it from injection to Weber carburetors.  Oh, three pumps on the pedal and it fired right up 

[Jackk]

Pumping the throttle is a great way to burn your airplane down

 

 

Does your POH say to pump the throttle for a carbureted engine?

[hammdo]

Yes, mine does, 2 to 3 times when cold…, 1 time when hot usually works on mine… throttle 1/4 open - mixture on mine is about half open. Starts right up….

[Vance Harral]

54 minutes ago, Jackk said:

Pumping the throttle is a great way to burn your airplane down

When done carelessly, yes.  But this is sorta like saying, "Flying a taildragger is a great way wreck an airplane in a ground loop".  We accept certain risks in order to operate certain airframes, and that's just the way it is.  For better or worse, many carbureted airplanes - including the Mooney M20C and M20G - have no way to prime the engine for start other than throttle pumping, and explicitly prescribe the practice in their operating manual.