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M20 C Engine Start problems


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1 hour ago, M20Doc said:

It takes fuel, air and sparks to make it run, I think your trouble is sparks.

If the engine fires/starts as you release the key from the start position, that's good evidence the SOS is not working properly.

Reference:  http://www.donmaxwell.com/publications/MAPA_TEXT/Shower of Sparks/Shower of Sparks.htm

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Just now, Mooneymite said:

If the engine fires/starts as you release the key from the start position, that's good evidence the SOS is not working properly.

It's also a sign of a bad left magneto. When troubleshooting mine after it failed in flight, we did everything except pull the mag, then tried to crank it--rrrr, rrrr, rrrr, rrrr, let go of key and she fired and began to purr.

But check the SoS first, it's much easier and cheaper! 

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7 pumps to start an M20C!?!?  If I did that I'd have a puddle of fuel on the ground.

1 pump- summer.  2 pumps- winter (after preheat).  Throttle cracked less than 1/4".  Engine starts on the 2nd prop blade.

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Had the same issue years ago... I would pump throttle a half dozen times and cross my fingers. The cooler the day, the harder it was to start. My IA pulled my carb, found a clogged accelerometer pump. Cleaned with solvent (now squirts like a water pistol) and reinstalled. Now cranks with no more than 3 pumps on the coldest day.. Check for a clogged accelerate fuel pump.


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3 hours ago, jejiii said:

Had the same issue years ago... I would pump throttle a half dozen times and cross my fingers. The cooler the day, the harder it was to start. My IA pulled my carb, found a clogged accelerometer pump. Cleaned with solvent (now squirts like a water pistol) and reinstalled. Now cranks with no more than 3 pumps on the coldest day.. Check for a clogged accelerate fuel pump.


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^^^^^^^^^^

+1

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  • 3 weeks later...

I agree not the "it should not take 6to 10 pumps... 3cold and 1 to 2 warm..  if your not dripping fuel out the bottem of the air box after 10 then your acc pump is not working correct.  I will say after repairing my shower of sparks every year (needed a new condenser) I talked the misses into letting me get the Slick Start.. that thing made sparks from my SP cable 2 inches to the engine block... like lightning.. that and a new battery and I start in 2 blades every time.

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  • 1 month later...

A small update. We have had the accelerator pump tested and it works fine. Will check out the shower of sparks during the next scheduled maintenance.

I have several pilots fly the airplane as I don´t create enough flight time currently due to other comitments. It´s only two of us who have problems starting. What is weird though is that the other 3 each use totally different procedures to start it but get it to run every time.

One uses fuel pump on, wait for pressure build up, fuel pump off, pump 5-6 times and then engage the starter with throttle 1/4 inch open.

Another runs the fuel pump, does not prime at all but pumps the throttle slowly while cranking. Takes him 4-5 blades to start. That is my mechanic who does it this way.

I think the problem has to do with too few fuel in the engine when I do it. I am scared of carb fire so I did maybe not prime enough. I will try the method my mechanic suggested and see what I can achieve.

Thanks for the tips regarding clogged pump. Will have that checked yet again.

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Glad to hear at least the accelerator pump has been eliminated as a cause.  However there's  still something not right.  In my experience, the O-360 should start in 2, or 3 blades with 2 pumps of the throttle any time OAT is 70 (21C), or above.

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10 hours ago, Urs_Wildermuth said:

Another runs the fuel pump, does not prime at all but pumps the throttle slowly while cranking. Takes him 4-5 blades to start. That is my mechanic who does it this way.

I think the problem has to do with too few fuel in the engine when I do it. I am scared of carb fire so I did maybe not prime enough. I will try the method my mechanic suggested and see what I can achieve.

Generally speaking, you don't need to worry about a carburetor fire if you pump while cranking.  The intake strokes are more than sufficient to pull the fuel into the cylinders.

I worry when I hear about people pumping 5-6 times before cranking.  That's a lot of fuel to shoot into the intake and then have gravity drop it back into the carburetor, just waiting for heat or a back fire to spark it off.

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I was in the pressurize and pump, Let evaporate, and start...camp.

It was definitely OAT dependent.

I built my procedure one datapoint at a time.  

Same process works for starting the IO550. Instead of counting pumps, count one-Mississippis, while the fuel pump primes the system...

Best regards,

-a-

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6 minutes ago, carusoam said:

 

Same process works for starting the IO550. Instead of counting pumps, count one-Mississippis, while the fuel pump primes the system...

Biggest difference is that in the IO-550, the fuel is pumped into the intake manifold at the cylinder head.  In the carbureted O-360, it is squirted vertically at the intake manifold, where gravity takes over and it drops down, through the carburetor, to the carburetor air box, where it pools awaiting an ignition source.

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Try getting more aggressive with the ignition key, the SOS backfeeds through the switch and if some pilots are not pushing hard enough (to fully engage the contacts) the spark might not reach the proper mag. Is the front wheel soaked in fuel?  With mine anything over two pumps is reaching the tire in warm temps. 

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When pumping the throttle, the fuel stream from the accelerator pump hits the closed throttle plate, once it opens wide enough the fuel hits the top of the intake manifold.  In both case fuel runs back down the throat of the carburetor and into the airbox.

As Andy points out pumping while cranking reduces the dangers of a carb fire.

Mooney should have installed a standard engine primer.

Clarence

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My 67C starts every time with 3 pumps of the throttle if cold and two if hot. Fuel pump on, wait for pressure to stabilize then pump throttle 3 times and turn fuel pump off. Turn key and she fires within 2 blades every time.


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  • 2 months later...

Undigging this old thread.

The saga went on and on and nobody took the two pilots to whom the start up problems continuously happened. Then one day one of those who never had a problem and was looking at us with suspicion got hit as well. Only he never managed to start it at all.

In the end, it now appears that the ignition lock is broken intermittedly. We did order a new one and are waiting for the results. This was found out when the engine started just when someone gave up and released the key from the starter position. Don Maxwell has apparently written an article describing exactly this.

 

Will let you guys know once the new lock is installed.

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2 minutes ago, Urs_Wildermuth said:

This was found out when the engine started just when someone gave up and released the key from the starter position. Don Maxwell has apparently written an article describing exactly this.

Yep.  Classic symptom of a bad shower-of-sparks box.  I posted the link to Don Maxwell's article several posts ago.

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I always thought that the engine starting with release of the key pointed to a bad left mag. After troubleshooting my own in-flight left mag failure, pulling plugs, checking that everything was tight, she did nothing but turn over nicely with no trace of firing. When I let go of the key, she immediately starting running smoothly. Disassembly of the left magneto [wish I had thought to take a picture! but I was AOG 3 hours from home] showed that the condenser wire had been cut in two by the big gear, and there was signs of internal arcing. The left mag did nothing at all, but the engine started nicely on the right when letting the key come off of "START" and back to "RUN" with it turning over.

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  • 1 month later...

Well guys, I have to say this story gets me to the point where I really am getting totally frustrated.

The aircraft has had extensive maintenance to the systems of the engine now. It has had it's left magneto overhauled, it has a new ignition lock and key, the shower of sparks box was thoroughly tested and found ok. Until we had all the parts and with Xmas and New Year in between, 2 months down time.

After all was being put together, the maintenance guys tested the engine. It fired on the first try. Every time. For one whole week. One of my pilots flew the airplane back, also there, nothing noteworthy.

Due to closure of the airport, the airplane has been sitting out for now about 2 weeks. Today, the same guy who took it from the maintenance wanted to go flying.

Well, the engine did not fire. Zero, Nada, Nothing. Tried on the internal battery first, then on a strong external one. Starter turns pure vanilla, but there is NO sign of the darn thing firing. Not once in almost a full hour of trying.

What the hell is wrong with this Lycosaurus? It is a bog standard O360 and we did everything Don Maxwell said we should in his great article, it works GREAT when maintenance test it (and they do nothing else then what we do) and now this?

 

I am running out of ideas and money and wonder what the hell to do. The airplane is now again standing at a no maintenance airport and getting the mechanics through security is next to impossible. We can't get the engine running which means we can't ferry the plane back to maintenance and even if we did, I am sure it would work fine there.

Any ideas are appreciated. I am thourougly out of them.

 

 

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Urs any challenges with the usual stuff like OAT, pre heat, and prime?

What are the methods of testing the shower of sparks in the field?  To verify the old challenge hasn’t resurfaced... like a loose or broken wire from the new switch...

Best regards,

-a-

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A good preheat helps when temps are below ~40°F (4°C). I have an oil pan heater, and an hour is usually fine. Then I turn the prop by hand about 2-3 revolutions. Going through the prestart checklist, after pumping the throttle 4-5 times, I put on and adjust my headset, wind and set the clock, just to kill a minute so the cold fuel just dumped into the carburetor can vaporize. Then crank away.

If it doesn't start pretty quick, pump the throttle while cranking. 

Good luck solving this!

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Fuel valve open with pressure building with the boost pump?  

Crank for 2 seconds and let the key go not working?

There is some variation in starter switches and the number of connectors they have in back.  You need to make sure both the SOS and starter are getting power when you push in the key.

 

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Urs any challenges with the usual stuff like OAT, pre heat, and prime?
What are the methods of testing the shower of sparks in the field?  To verify the old challenge hasn’t resurfaced... like a loose or broken wire from the new switch...
Best regards,
-a-
Temps are 10C and more so preheat is not a issue. How the box was tested I don't know but the folks at maintenance usually know their stuff. But I will insist on a new one now. Still why does it work there?

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On 29.1.2018 at 4:02 AM, MIm20c said:

Fuel valve open with pressure building with the boost pump?  

Crank for 2 seconds and let the key go not working?

There is some variation in starter switches and the number of connectors they have in back.  You need to make sure both the SOS and starter are getting power when you push in the key.

 

First line, yes absolutey. We did check the priming and fuel flow a while ago. Also, when we continue to trying to start it, it starts dripping out on the tire, so eventually there is too much fuel..

2nd, no.

3rd: Well, what does drive us totaly crazy is that after the maintenance action, they did test it THOROUGHLY. That is, the plane stood there for a week until we picked it up and it started every day without ANY problems. On the ferry flight, it started as well, obviously.

So what we are looking at is an intermittent problem, which is very hard to locate. I am almost sure that IF we can get it to start and ferry it back to maintenance, it will work again perfectly all the time there. So what to do?

I am starting to wonder whether to replace ALL the wiring concerned but I understand this is a very expensive job, as it means basically rewiring the whole engine?

 

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