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M14P Magneto

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flyayak

Joined: 17 Jul 2010
Posts: 7

Posted: Sat Jul 17, 2010 10:10 pm Post subject: M14P Magneto

Hi YAK-Folks,



first of all I want to thank you all for this great forum. It helps me a lot to solve several problems with my YAK 52 in the past.

Now I have a question to all of you M14P experts.

A few weeks ago, while riding in my YAK with 82% and climbing, after 20 minutes the engine stops two times short one after another only for a heartbeat. I stopped climbing immediately and closed the throttle. After that, I noticed a loss of power, while the engine runs smooth again. After checking the mags, with no noticeable problems I went back to the airfield, landed and while shutting down the prob it turned backwards a few cycles, which it hasnÂ´t done for the last 120 hours. I pulled the plugs (Dennisâ€™ automotive conversion kit was installed two years ago and the plugs were till the last 30 hours) and they have showed a white surface, so it seems that the mixture was too lean. Therefore I changed the diaphragm of the carb, which was already inside since the last 25 years (!). It looks a bit crumpled but without any cracks.



While test running the engine after this with the cowling off, it runs great on ground and shows every values in an acceptable range. After putting the cowling back on again I did a test run again and while switching to magneto #2 it stops intermittently for a second or so and shows also on both magnetos an excessive drop of rpm, that means round about 6-7%. It was a very hot day with outside temperatures of about 36Â°C. At the moment it is very hot in Germany....



So, my question is, is it possible, that both coils in the mags went TU (I like this expression ) while the engine get (very) hot? Any other advices?



Thanks a lot in advance.



Best regards

Stefan

viperdoc(at)mindspring.co
Guest

Posted: Sun Jul 18, 2010 6:33 am Post subject: M14P Magneto

Stefan,

Having riden that horse a couple of times, the senerio generally goes like this. You have been airborne for about 15 to 20 minutes when there what sounds like a backfire with the engine stopping for a heartbeat then resumes power as if nothing happened. Airborne mag checks do not show any real issues. If you continue to fly this process will intermitantly repeat itself with the same results. 

Check of the plugs and the timing on the ground will not turn up the problem unless you run the engine at nominal one or above for 15 to 20 minutes. That is not practical since that will overheat the engine.

The problem most likely is in the mags and it is indeed a TU coil. The paper capacitor has failed but it takes a while for the coil to heat up facilitating a discharge that is transmitted to each plug on the bank resulting in spark that explodes the fuel air mixture in the supercharger via the open intake valve on that cylinder.

Hope this helps.



--

pilotdog57(at)aol.com
Guest

Posted: Sun Jul 18, 2010 6:33 am Post subject: M14P Magneto

I had exactly that problem with my M14P powered CJ- even the mag drop. After chasing it around as a mag problem it ended up being a blocked header tank vent- causing severe lean conditions ( white plug deposits) and stopages in flight with erratic mag checks after flight. Try checking your vents before disassembling your mags. It does not take much to block the vents. The hotter the day the more the problem will manifest itself because of expanding air in the header tank cutting off the fuel.

Doug Zeissner

Sent from my Verizon Wireless BlackBerry



--

flyayak

Joined: 17 Jul 2010
Posts: 7

Posted: Sun Jul 18, 2010 11:50 am Post subject: Re: M14P Magneto

Thank you for your fast reply.

Doc: I read about the problem with the mags in the forum which will only occur if the engine is hot after 20-35 min. of flying. This and the mag drop/interruption was the reason why it comes into my mind, that there could be a problem with the mags.

Doug: You talk about the header tank vents. This means the flapper valves on both sides connected to the main tanks, right? Sorry, because of my English, but it isnÂ´t good enough and my dictionary tell me that vent and valve there are two different meanings. If I understand it right, you mention that if the pressure in the header tank is to high and the valves are not in a good condition, there is not enough fuel flow from the main tanks to the header tank? Is it possible to check them without dismounting the header tank?

Thanks 

Stefan

pilotdog57(at)aol.com
Guest

Posted: Sun Jul 18, 2010 2:21 pm Post subject: M14P Magneto

Stefan-

On the CJ the two main tanks gravity feed to a small header tank. The outlet for the header tank is about 2/3 to 3/4 up from the bottom of the tank. This makes the header tank also a sump for water and other contaiminates. There is always a little area of air in the top of the header tank. When the vent line for the header is blocked that air bubble can not regulate itself and expands with any increase of temperture and/or altitude. That increased air bubble can interfere with fuel flow- it can do it in ways that mimic some magneto problems. It is easy to drain the fuel and with two people disconnect all the fuel vents and using appropriately sized tubing attached to the exposed vent line end either blow into or use VERY light air pressure to check that the vent lines are clear. Now it may still be a magneto problem- others have had similar symptoms and had different solutions- but a blocked header tank vent is what I had and finding the blockage fixed my problem. I had huge mag drops on the ground after a flight, sudden stoppages and restarts in the air with rough operation soon after that smoothed out eventually, and lean conditions no matter how the carb was adjusted. This problem took a long time to figure out, it did not happen every flight, and the higher and hotter the conditions the worse it would be.

Doug Z

---

tigeryak18t

Joined: 26 Sep 2009
Posts: 233
Location: PARIS FRANCE

Posted: Sun Jul 18, 2010 2:54 pm Post subject: M14P Magneto

Hi all,



regarding the tank vents. If I am not wrong there are three vents. Left tank, right tank and header tank. If you blow the vents with compressed air then you will have to take a lot of care that this air can go away. In the case of the left and right tank it is easy because you just have to open the tank before blowing the vent. In the case of the header vent then you may be carefull because if you blow it without opening the purge you will dammage the valve in the header tank....as I have been told....

  My mechanical words are perhaps not the god one but still the result would be the same...take all precautions before blowing the vents.

Perhaps Dennis or Doug could drop a word about this manipulation. All of us would like to be sure that our tank have a good connection to the air but if we try to blow air let us just do it the right way.

  



g'night

Didier



2010/7/18 flyayak <sschne3082(at)aol.com (sschne3082(at)aol.com)>

 	  Quote: 	
		    --> Yak-List message posted by: "flyayak" <sschne3082(at)aol.com (sschne3082(at)aol.com)>

 

 Thank you for your fast reply.

 Doc: I read about the problem with the mags in the forum which will only occur if the engine is hot after 20-35 min. of flying. This and the mag drop/interruption was the reason why it comes into my mind, that there could be a problem with the mags.

   Doug: You talk about the header tank vents. This means the flapper valves on both sides connected to the main tanks, right? Sorry, because of my English, but it isn´t good enough and my dictionary tell me that vent and valve there are two different meanings. If I understand it right, you mention that if the pressure in the header tank is to high and the valves are not in a good condition, there is not enough fuel flow from the main tanks to the header tank? Is it possible to check them without dismounting the header tank?

   Thanks

 Stefan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=305339#305339

 

 

 

 

 

 

 

 ===========

 rget="_blank">http://www.matronics.com/Navigator?Yak-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 	


-- 

Didier BLOUZARD

didier.blouzard(at)gmail.com (didier.blouzard(at)gmail.com)

0624243672

 

  [quote][b]

_________________
Didier Tiger YAK18T
Member of Commemorative Air Force
French Wing

pilotdog57(at)aol.com
Guest

Posted: Sun Jul 18, 2010 3:19 pm Post subject: M14P Magneto

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">   Didier-You are correct about not using too much pressure on the fuel tanks. We drained all of the fuel, diconnected the vent lines, removed the fuel caps, and the bottom sump fixture from the header tank. We used surgical tubing to connect to the ends of the vent tubes- this allowed one to get to the vent tube ends- and either blew into them or used only around 2 psi (1/10 atmos) to find the blockage. When the blockage was isolated we took great care not to pressurize any of the fuel tanks by having everthing open and the ends of the vents fully disconnected. Then we blew out the blockage with 100 PSI air (7 atmos). It can take only about 5 psi to ruin your aluminum tanks... So be carefull.Doug Zeissner

Sent from my Verizon Wireless BlackBerryFrom:  Didier Blouzard <didier.blouzard(at)gmail.com> 

Sender:  owner-yak-list-server(at)matronics.com 

Date: Mon, 19 Jul 2010 01:53:53 +0300

To: <yak-list(at)matronics.com>

ReplyTo:  yak-list(at)matronics.com 

Subject: Re: Yak-List: Re: M14P Magneto

Hi all,

regarding the tank vents. If I am not wrong ther= e are three vents. Left tank, right tank and header tank. If you blow the v= ents with compressed air then you will have to take a lot of care that this=  air can go away. In the case of the left and right tank it is easy because=  you just have to open the tank before blowing the vent. In the case of the=  header vent then you may be carefull because if you blow it without openin= g the purge you will dammage the valve in the header tank....as I have been=  told....

  My mechanical words are perhaps not the god one but still the result w= ould be the same...take all precautions before blowing the vents.

Perhaps Dennis or Doug could drop a word about this manipulation. All of u= s would like to be sure that our tank have a good connection to the air but=  if we try to blow air let us just do it the right way.

g'night

Didier

2010/7/18 flyayak <[url=m= ailto:sschne3082(at)aol.com]sschne3082(at)aol.com[/url]>

 	  Quote: 	
		    --> Yak-List message posted by: "flyayak" <[url=mailt= o:sschne3082(at)aol.com]sschne3082(at)aol.com[/url]>

 Thank you for your fast reply.

 Doc: I read about the problem with the mags in the forum which will only oc= cur if the engine is hot after 20-35 min. of flying. This and the mag drop/= interruption was the reason why it comes into my mind, that there could be = a problem with the mags.

   Doug: You talk about the header tank vents. This means the flapper valves o= n both sides connected to the main tanks, right? Sorry, because of my Engli= sh, but it isn=B4t good enough and my dictionary tell me that vent and valv= e there are two different meanings. If I understand it right, you mention t= hat if the pressure in the header tank is to high and the valves are not in=  a good condition, there is not enough fuel flow from the main tanks to the=  header tank? Is it possible to check them without dismounting the header t= ank?

   Thanks

 Stefan

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=3D305339#305339<= /a>

 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

 rget=3D"_blank">http://www.matronics.com/Navigator?Yak-List

 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

 http://forums.matronics.com

 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

 le, List Admin.

 =3D"_blank">http://www.matronics.com/contribution

 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

-- 

Didier BLOUZARD

didier.blouzard(at)gmail.com

0= 624243672

  [quote][b]

mikspin

Joined: 12 Aug 2007
Posts: 66

Posted: Sun Jul 18, 2010 11:00 pm Post subject: Re: M14P Magneto

Stefan,



Where are you in Germany?



Mike Hastings

arthur.white(at)gmail.com
Guest

Posted: Sun Jul 18, 2010 11:53 pm Post subject: M14P Magneto

Stefan

  

 I do not know if this will help but it may save a coil or mag change.

  

 I had an identical problem, engine stopping for a moment then picking up, but only when hot and in flight, not reproduced on the ground except after an in flight event.

  

 We changed the coil, changed the cigarette in the mag and checked the plugs,  In the end we looked in the high tension cable insulation and the bottom two cylinder cables where wet with an oilly watery fluid.

  

 The theory is that the fluid was static in the insulation on the ground and most of the HT lead dry, but in flight especially during aerobatic the fluid ran back and caused the engine to stop for short periods.

   

 I hope this helps.

  

 And thanks to my friends Jan and Christian for working this problem.

  

 Arthur

 On Sun, Jul 18, 2010 at 8:10 AM, flyayak <sschne3082(at)aol.com (sschne3082(at)aol.com)> wrote:

  	  Quote: 	
		  --> Yak-List message posted by: "flyayak" <sschne3082(at)aol.com (sschne3082(at)aol.com)>

 

Hi YAK-Folks,



first of all I want to thank you all for this great forum. It helps me a lot to solve several problems with my YAK 52 in the past.

Now I have a question to all of you M14P experts.

A few weeks ago, while riding in my YAK with 82% and climbing, after 20 minutes the engine stops two times short one after another only for a heartbeat. I stopped climbing immediately and closed the throttle. After that, I noticed a loss of power, while the engine runs smooth again. After checking the mags, with no noticeable problems I went back to the airfield, landed and while shutting down the prob it turned backwards a few cycles, which it hasn´t done for the last 120 hours. I pulled the plugs (Dennis’ automotive conversion kit was installed two years ago and the plugs were till the last 30 hours) and they have showed a white surface, so it seems that the mixture was too lean. Therefore I changed the diaphragm of the carb, which was already inside since the last 25 years (!). It looks a bit crumpled but without any cracks.

 

While test running the engine after this with the cowling off, it runs great on ground and shows every values in an acceptable range. After putting the cowling back on again I did a test run again and while switching to magneto #2 it stops intermittently for a second or so and shows also on both magnetos an excessive drop of rpm, that means round about 6-7%. It was a very hot day with outside temperatures of about 36°C. At the moment it is very hot in Germany....

 

So, my question is, is it possible, that both coils in the mags went TU (I like this expression ) while the engine get (very) hot? Any other advices?



Thanks a lot in advance.



Best regards

Stefan

  



Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=305269#305269

   

 ties such as List Un/Subscription,

 www.matronics.com/Navigator?Yak-List" target="_blank">http://www.matronics.com/Navigator?Yak-List

 ronics.com/" target="_blank">http://forums.matronics.com

 Matt Dralle, List Admin.

 =====



	
 

-- 

Best regards



Arthur.

  [quote][b]

viperdoc(at)mindspring.co
Guest

Posted: Mon Jul 19, 2010 5:08 am Post subject: M14P Magneto

Answer, start simple and work your way forward. Shot gunning the problem may get you an answer but you do not know what the exact thing was that fixed the problem. Admittedly, it will mean doing one thing taking the plane up over the airfield in gliding distance in case you loose the motor entirely. This being each time you make a change.   

Having gone through that with about a month of sphincter tightening experiences like momentary lose of power at 20 min to a rough spitting and sputtering engine barely making power as I was gliding down from 3500 ft. to two idiots bantering on the radio (CTAF) while  trying to make an emergency landing.   

The problem was fixed by changing the mag coil on #2. That all being said that may not be your problem. If you want to solve the crappy plug wire issue while you are at it, change to the Taylor plug wire and auto plug conversion. Check your timing but do you know yet which mag ran rough in the air? If so, I would look at that one closely maybe even checking the points setting, look at the distributor cap for arcing. If you want to be really obsessive, ohm out each plug wires. The but is you have a lot of places to look. Having gone through this a couple of times changing the coil was the answer for me.  

Doc  

     

From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Arthur White

 Sent: Monday, July 19, 2010 2:53 AM

 To: yak-list(at)matronics.com

 Subject: Re: M14P Magneto  

  

     

Stefan  

    

   

    

I do not know if this will help but it may save a coil or mag change.  

    

   

    

I had an identical problem, engine stopping for a moment then picking up, but only when hot and in flight, not reproduced on the ground except after an in flight event.  

    

   

    

We changed the coil, changed the cigarette in the mag and checked the plugs,  In the end we looked in the high tension cable insulation and the bottom two cylinder cables where wet with an oilly watery fluid.  

    

   

    

The theory is that the fluid was static in the insulation on the ground and most of the HT lead dry, but in flight especially during aerobatic the fluid ran back and caused the engine to stop for short periods.  

    

   

    

I hope this helps.  

    

   

    

And thanks to my friends Jan and Christian for working this problem.  

    

   

    

Arthur  

    

On Sun, Jul 18, 2010 at 8:10 AM, flyayak <sschne3082(at)aol.com (sschne3082(at)aol.com)> wrote:  

--> Yak-List message posted by: "flyayak" <sschne3082(at)aol.com (sschne3082(at)aol.com)>

 

 Hi YAK-Folks,

 

 first of all I want to thank you all for this great forum. It helps me a lot to solve several problems with my YAK 52 in the past.

 Now I have a question to all of you M14P experts.

 A few weeks ago, while riding in my YAK with 82% and climbing, after 20 minutes the engine stops two times short one after another only for a heartbeat. I stopped climbing immediately and closed the throttle. After that, I noticed a loss of power, while the engine runs smooth again. After checking the mags, with no noticeable problems I went back to the airfield, landed and while shutting down the prob it turned backwards a few cycles, which it hasn´t done for the last 120 hours. I pulled the plugs (Dennis’ automotive conversion kit was installed two years ago and the plugs were till the last 30 hours) and they have showed a white surface, so it seems that the mixture was too lean. Therefore I changed the diaphragm of the carb, which was already inside since the last 25 years (!). It looks a bit crumpled but without any cracks.

 

 While test running the engine after this with the cowling off, it runs great on ground and shows every values in an acceptable range. After putting the cowling back on again I did a test run again and while switching to magneto #2 it stops intermittently for a second or so and shows also on both magnetos an excessive drop of rpm, that means round about 6-7%. It was a very hot day with outside temperatures of about 36°C. At the moment it is very hot in Germany....

 

 So, my question is, is it possible, that both coils in the mags went TU (I like this expression ) while the engine get (very) hot? Any other advices?

 

 Thanks a lot in advance.

 

 Best regards

 Stefan    



 

 

 

 Read this topic online here:  

  

http://forums.matronics.com/viewtopic.php?p=305269#305269    

ties such as List Un/Subscription,

 www.matronics.com/Navigator?Yak-List" target="_blank">http://www.matronics.com/Navigator?Yak-List

 ronics.com/" target="_blank">http://forums.matronics.com

 Matt Dralle, List Admin.

 =====

 

 

   

  

  



  

 -- 

 Best regards

 

 Arthur.   	  Quote: 	
		    http://www.matronics.com/Navigator?Yak-List 	
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       [quote][b]

dsavarese0812(at)bellsout
Guest

Posted: Mon Jul 19, 2010 5:33 am Post subject: M14P Magneto

If you decide to make the automotive plug conversion, I  have the kits in stock.  Contact me off-list for further info.

 Dennis

  

 [quote]   ---

mark.bitterlich(at)navy.m
Guest

Posted: Mon Jul 19, 2010 7:23 am Post subject: M14P Magneto

As a Tech Rep, my rule of thumb when there is a problem is to always go where people last were putting their hands on something.  It usually works.  



You may actually have TWO problems.  If you go looking for just one thing that will cause EVERY problem you have listed, you may end up driving yourself nuts.  So as Doc was alluding to, take one problem at a time.  I have seen bad fuel cause my M-14P to run backwards when I shut off the mags.  It also happened a few times when I tried running various grades of automotive fuel mixed with 100LL Av-Gas.  So, the engine running backwards a few blades may not be related to the MAGS at all, but instead to a bad load of fuel.  Also.... Remember that water in the fuel, or again just BAD fuel, could cause the engine to spit and sputter in flight.  And bad fuel is a really easy thing to overlook.  You also could have a restriction in the fuel line.  Did you happen to eye-ball that fuel pressure gage when all this was going on?  There are a lot of stories on the YAK list of people finding all manner of things in fuel lines, and ... Just off the cuff, it appears to me that you actually acknowledged that the engine might be running lean, tried a corrective procedure, and maybe what you tried to fix was never the problem to begin with.  I.E  Your engine may still possibly be running lean.  With no EGT indications, it is pretty hard to really tell right NOW, how rich or lean that engine really is.  The carb barostat could easily be at fault.  



Anyway, a lot of what you are talking about sounds fuel related to me.  Or rather, it sounds like it COULD be fuel related. 



Repeat your test with the one mag that runs badly.  While it is running badly, just for the heck of it, turn your primer handle to the prime position.  Do not pump it or pull it out.  Just turn it to the prime position.  This will cause the engine to run REALLY rich.  See if all of a sudden your engine now is running perfectly with no missing.  If it does, you don't have a mag problem.  If it continues, you probably do have a mag problem, test accordingly.  



No, I don't think two coils from two mags would ever go Tango Uniform at the same time.  Of course anything is possible, but this is pretty unlikely.  



My gut feeling is that you have a fuel issue and maybe one bad mag.  But this is just a wild guess.  



Mark Bitterlich

  



 



--

flyayak

Joined: 17 Jul 2010
Posts: 7

Posted: Mon Jul 19, 2010 10:35 am Post subject: Re: M14P Magneto

O.k., I realized that this issue can have a lot of different reasons.

Today, I worked further on the issue. After a further test run, which shows the said excessive drop of rpm and a rough running on mag #2 and back cycling of the prop after shutting down, I pulled all the spark plugs and replugged them to the advised .020 (as I said I already have the automotive conversion kit in). They were gapped to round about .030. I also removed the distributor cap from magneto #2 and cleaned all parts inside, especially the spring which holds the cigar down. This one shows a lot of corrosion. I had a similar problem a few time ago on mag #1 which prevents the engine from starting because of a loss of high tension from the starting coil.

After that the engine runs very well on ground and shows only round about 2% loss of rpm on both mags.

O.k., I understand, that the coil in mag #2 can be nevertheless bad, but tomorrow I will put my nappy's on and start I test flight above the airfield.



The issue with the mixed/bad fuel is also a good hint, because at the moment I have a mixture of  car fuel and avgas in it.



Stefan

(from the southern part of Germany near Munich)

cjpilot710(at)aol.com
Guest

Posted: Mon Jul 19, 2010 2:05 pm Post subject: M14P Magneto

If you have the original ignition harness, this could be your problem.  I literally chase "mag/plug" for months and months.  It (the ignition harness) finally gave up entirely high over Americas GA. on the way to an airshow.  A young crop duster mechanic with a southern draw so long that it took him forever to tell me he thought it was the harness.  He did a test, sure enough that was it. I spent the night and sent off for Dennis' auto plug / harness and have had NO problems since.

    

   The original ignition harness's on the M-14 is well built for 1940's technology, but the insulation on the wire will break down over time and use.  It can be intermittent, and will give every indication similar to a mag/ coil or plugs.  I really believe that 90% of the problems I had were due to the gradual break down of the harness.

    

   Jim "Pappy" Goolsby

    

    

 

 

   

 

 

   --

mark.bitterlich(at)navy.m
Guest

Posted: Mon Jul 19, 2010 2:34 pm Post subject: M14P Magneto

ABSOLUTELY DARN SKIPPY.  DEAD ON CORRECT.  



For those in Europe, there is a kit where you can replace the original Russian wire with silicone wire.  PAIN IN THE TAIL to install.  Did it once.  Never again.  Of course you also have to install new cigarette ends on each wire, etc., etc.  Not a lot of fun.  But, it does keep it legal (for Europe).  I think Richard Goode probably knows all the details on that. 



Mark Bitterlich



P.S.  Stephan.... Plug gap using the kit you are now using is important.  Something to keep in mind ...  And I have said this already in a different message string.  A wider gap takes more voltage to jump.  The usual failure mode of Mag coils is that the insulation breaks down and they short.  This can also be exacerbated by heat.  The wider the gap, also causes more heat in the coil.  Going from .030 to .020 may have indeed solved your most immediate problem, but realize that you might just have lowered the internal temp, and voltage requirements of an already weak coil, just enough to allow it to work well again.  If I were you, I'd try to obtain a coil to keep handy, or a whole mag for that matter.  



Yes, my personal M-14P tended to stop and "kick back" when run with auto-fuel.  I am sure it had something to do with fuel mixture, vapor pressure, outside temp, timing, whatever.  But be aware of this.... It did that once and sheared the generator coupling shaft..... as in POOF.  It is NOT a good thing to allow to continue to happen.  It doesn't take a lot of headwork to realize that any spinning mass that suddenly reverses direction puts a tremendous strain on the parts.  Generator, mags, you name it.. Not to mention engine internals.   

 



--

flyayak

Joined: 17 Jul 2010
Posts: 7

Posted: Tue Jul 20, 2010 11:20 am Post subject: Re: M14P Magneto

Hi all,



just for information. Today it was possible to reproduce the failure on a ground run after a few minutes while the engine was warmed up.

As most of you supposed, itÂ´s a bad coil in magneto #2.



Thanks again.

Stefan

viperdoc(at)mindspring.co
Guest

Posted: Tue Jul 20, 2010 11:51 am Post subject: M14P Magneto

Glad you did not have to fly her to reproduce it. Life's to short for to

many sphincter tightening experiences.

doc



--

Vic

Joined: 12 Aug 2008
Posts: 115
Location: Southern Bavaria

Posted: Tue Jul 20, 2010 4:35 pm Post subject: Re: M14P Magneto

Hi Stefan,



you may have one faulty coil in the mag, but white spark plugs are no symptom of a shot coil - the contrary. As you said you are running the Yak on part auto fuel. And we had real trouble with that in hot weather - no take-off at 100 % power possible in the 18 T . A fill-up with avgas  helped, no other actions required. So the real problem was vapour bubbles in the fuel pump at high rpm. As this pump is not particularly good in sucking we added an electric pump in front of the service tank to feed the engine-driven pump. This Pierburg pump should deliver ~100 liters per hour at 0,5 bar nominally, but was at its limit in times, so we added another one for safety and since we never had a drop in fuel pressure to critical limits when using pure auto fuel for some years now. YouÂ´d be lucky to find avgas at 10 Dollars per gallon these days in our continent and this wonÂ´t be getting better we feel ... 

 So, Stefan, please watch the fuel pressure closely on the take-off run or static at minimum 80 or 90 % power. If you leave the plane a few hours in the sun to heat the fuel in the tanks you might observe a dramatic effect on fuel pressure ... We remember Franz U. had a moment when taking off in A. airfield last year in  his 18 T so we just cannot believe there are not more reports from other Yakkers confirming this behaviour on mogas in hot weather.

 Most "modern" low wing aircraft have electric fuel pumps required for take-off  and landing as a safety feature, so we definitely like to suggest installing an electric pump on any Yak for added safety. The picture below shows the system in our 18 T, another one-way valve added for the electric pumps.

 To check the tank vents : You could plug all vents and open the drain valve under the fuselage : The fuel flow should stop in a short time. Then open one plug and watch the flow - satisfied with the amount of fuel ? OK, plug the vent and open the other one, the flow rate should be the same.  It is unlikely that all vents should be blocked, so the Yak should run OK on one tank alone - and it should run on one mag as well with negligible power reduction. So we suspect a mogas effect.

  Apart from that - Stefan, time to see us once again.



         Helga and Vic

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