Starting problems 1968 M20G

[Dwb62]

I bought this plane last May, starting procedure for cold start was to pump throttle twice and crack open the throttle and start. It usually started within a few turns. Now recently the last few times it is not firing up like that. Went out last week I tried to start it 4 times, nothing is working, I was about to give up before I ran the battery down, and I tried one more time and it started running almost instantly. I was going to have an A&P look at this week, anybody know what could be causing this problem. Thanks 

[Shadrach]

25 minutes ago, Dwb62 said:

I bought this plane last May, starting procedure for cold start was to pump throttle twice and crack open the throttle and start. It usually started within a few turns. Now recently the last few times it is not firing up like that. Went out last week I tried to start it 4 times, nothing is working, I was about to give up before I ran the battery down, and I tried one more time and it started running almost instantly. I was going to have an A&P look at this week, anybody know what could be causing this problem. Thanks 

Does it have impulse couplings or shower of sparks?

[Dwb62]

I don’t know, I will have to check that out.

[DXB]

52 minutes ago, Shadrach said:

Does it have impulse couplings or shower of sparks?

 

28 minutes ago, Dwb62 said:

I don’t know, I will have to check that out.

If a G model, it will be O-360-A1D with shower of sparks (unless left mag converted to electronic ignition - eg Surefly)

Be careful not to flood - more  than 6 or 7 total throttle pumps will pour out onto your front tire and create fire hazard .  If that happens clean it up and walk away for 30 minutes to let fuel vaporize, then use flooded procedure in POH

If its suddenly cold for first time where you are that's probably the reason - use ~3-4 pumps before cranking and one or two while you crank, or preheat - that helps enormously!  Don't keep pumping if its not working though....

Go easy on the starter - it's easy to fry it, dont crank for more than 15 sec or so.  

Further troubleshoot is basic fuel/compression/spark/timing consideration; formal lycoming guide helps https://www.lycoming.com/sites/default/files/attachments/SSP-475.pdf

Ross probably has some more focused tricks distilled from procedures in document, as will most any A&P.

I've been in this situation several times - the most interesting one was caused by a loose contact on the ignition switch after getting avionics work done

[Greg Ellis]

I had an issue much like this with my C model when I first bought it.  My issue was a worn out accelerator pump in the carburetor.  It is a leather type membrane that may wear out or break.  When it does, you cannot prime the engine and may take many, many blade turns to start if it ever did.  I wore the battery down one day trying to start it.  When the accelerator pump was repaired, the plane started on the first turn of the prop.

So, I think I would look electrical first like was said above but do not rule this out.

[Shadrach]

@DXB  It's the "started almost instantly" comment that gave me the impression that the SOS was not working which is why I wanted to verify ignition type.  The appearance of an "Instant" start happens when the key is released at just the right moment to the both position, the mag fires and the (well primed) engine starts immediately or it kicks back.

[Dwb62]

Thanks for your replies, I am leaning towards the shower of sparks being the problem because it goes from not even trying start to an instant fire up when it finally starts.if that is the problem would it be better to install a Surefly mag to replace it?

[Shadrach]

7 minutes ago, Dwb62 said:

Thanks for your replies, I am leaning towards the shower of sparks being the problem because it goes from not even trying start to an instant fire up when it finally starts.if that is the problem would it be better to install a Surefly mag to replace it?

Does your ignition have a "push" position like this one?

 

[Dwb62]

Yes, looks the same.

[DXB]

49 minutes ago, Dwb62 said:

Thanks for your replies, I am leaning towards the shower of sparks being the problem because it goes from not even trying start to an instant fire up when it finally starts.if that is the problem would it be better to install a Surefly mag to replace it?

Rarely is the SOS box itself truly the problem; it's not hard to replace if it is...though mounted in an awkward location on cabin side of the firewall.  I think what Ross is referring to is that you can crank it forever in start position and then it only fires immediately you give up and move it back to both position. That could be a dead SOS box, it also could be a problem with the left mag.  If you turn key to both without pushing in to engage the starter, you can hear the SOS buzz and likely that's fine.  If you don't hear the buzz its the SOS box, its connection to the battery, or its connection to the ignition switch. 

Surefly mags are great but you want to diagnose the problem first.  Here's a troubleshooting guide from Don Maxwell for the SOS system, which is a great system overall.

https://www.donmaxwell.com/shower-of-sparks

[Shadrach]

21 minutes ago, Dwb62 said:

Yes, looks the same.

First thing I would do is check to see if the starter vibrator is buzzing with the key in the start position.  That is to say with the key turned all the way to the right but not pushed in you should hear the high pitched buzzing sound of the energized starter vibrator. Note this has nothing to do with the engine's starter.

That's the first and least invasive check.

 

Attached is the manual for your SOS system.

 

SOS IgnitionVibratorManual.pdf

[Shadrach]

5 minutes ago, DXB said:

I think what Ross is referring to is that you can crank it forever in start position and then it only fires immediately you give up and move it back to both position. That could be a dead SOS box, it also could be a problem with the left mag.

Often an ignition switch issue and also sometimes a continuity issue from vibrator to retard breaker. Best to do the easiest, least invasive thing first.

[Dwb62]

Thanks guys for the info and downloads, I will go by the airport tomorrow and see if I can hear the starting vibrator buzzing or not, I will pass this information along to the mechanic, it might save time troubleshooting.

[Hector]

Assuming you checked the battery is good right? When I owned a C I could always tell when my battery started to go because instead of starting after two blades it would require 5 or more.


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[Dwb62]

Yes, battery turns the engine over good.

[Hank]

When the weather cools off, my starting procedure changes to this:

1. Master On
2. Boost Pump On until fuel pressure stabilizes, then Off
3. Pump throttle 3-5 times,  leave open ~1/2"
4. Mixture Rich
5. Wind and set yoke clock
6. Turn key and push
7. If no fire after first revolution, begin pumping throttle again while cranking
8. Let go of key when engine catches, or after ~15 seconds 

The colder it is, the more times I pre-pump the throttle, and the longer it takes to fire and catch.

Yes, I do this even after having the engine preheat turned on overnight. It worked in WV with single-digit morning temperatures, and it works here in Alabama with much friendlier low temps. 

[Shadrach]

16 hours ago, Hank said:

When the weather cools off, my starting procedure changes to this:

1. Master On
2. Pump throttle 3-5 times,  leave open ~1/2"
3. Mixture Rich
4. Wind and set yoke clock
5. Turn key and push
6. If no fire after first revolution, begin pumping throttle again while cranking
7. Let go of key when engine catches, or after ~15 seconds 

The colder it is, the more times I pre-pump the throttle, and the longer it takes to fire and catch.

Yes, I do this even after having the engine preheat turned on overnight. It worked in WV with single-digit morning temperatures, and it works here in Alabama with much friendlier low temps. 

Where does the boost pump fit in to this procedure?

[Hank]

5 minutes ago, Shadrach said:

Where does the boost pump fit in to this procedure?

Oops! This is why we use checklists instead of memory. I added it in above.

[Shadrach]

8 minutes ago, Hank said:

Oops! This is why we use checklists instead of memory. I added it in above.

Thanks!  I am trying to learn what is most common.  I don't have much time in C models.  All of the carbureted I flew in my early flying days had primer circuits.

I am curious as to why the mixture is enrichened after the throttle is pumped and not before. Does it cause it over prime?  In all of the carbed engines with primers that I operated years ago, mixture rich was the first step in the starting procedure. 

I'm not trying to nit pick, I'm trying to learn the idiosyncrasies of a set up that I don't often encounter. 

[Hank]

No, our carbureted Mooneys do not have primers. So I run the pump to maximize fuel pressure, and every pump of the throttle fuel pressure drops some, and the pause lets the fuel vaporize. Colder temp requires longer time to vaporize. 

This is how I learned. Maybe keeping the fuel pump running while starting would increase likelihood of flooding? Now you're gonna make me read the Owners Manual.