lasar/ mcfarlane throttle cable rigging

[jamesm]

Hi,

I installed  lasar Mcfarlane throttle cable in a 67C. The new throttle cable has the full range movement on the carburetor. The prop cable  rigging never was touched and was fine the throttle cable was original 55 year old cable. When I flew it, I had full power  on  take off but in cruise when went to  make  adjustments with throttle and  propeller my rpm dropped.  for example anything  below  about 24" MAP , 2400 rpm my rpm will drop. In other words, I can't get 24^2 or 23^2 or 20" MAP 2300 rpm  throttle/prop settings were done at approximately 2500 ft altitude. I was cross check the cruise  setting listed  in the owner manual aka POH. It was suggested to me to check  my induction system  for  possible  leaks, by backflow air through the carburetor air box. Then check for air leaks with either feeling   for air or soapy water on induction joints and look for bubbles. I did a quick  leak check today but didn't see any leaks but with a noisy air source it was hard to tell.

 

Any ideas,

James  '67C

[A64Pilot]

I can’t image that’s a throttle cable issue, I’d suspect prop governor, but that’s just a suspicion

[EricJ]

"Rigging" the throttle cable just means that there's about 1/8" of travel left at both stops.   In other words, the throttle hits wide-open at the carburetor stop a little before the cable reaches its limit, and it hits the idle stop at the carburetor a little before the cable reaches its limit.    If that is done, and you can attain wide-open throttle and also reach the idle stop (which should be verified at the carburetor, not at the user end of the control), with a little "cushion" of travel on each end, then the cable is rigged properly.   Any operational issues remaining are not due to the cable.

 

[jamesm]

The throttle cable  on my particular  year and model of  mooney. there is bracket comes  from  prop governor  housing and  then  extends has I believe  it's a AN742 clamp attaches to  throttle cable sheve.

[time_adc]

I also recently changed my throttle cable with new McFarlane. The old cable was pinched at the firewall pass through. Symptom was that the engine would not stay at low rpm, it would slowly increase. When going over bumps I could feel the knob on the throttle being tugged forward. I suggest you check this as well. 

[jamesm]

I will have to  keep eye  on it. I  haven't  seen it  do the  low rpm  throttle  position creep.

[jamesm]

Problem Solved... After thinking on it a bit. I had recalled that I had similar situation many years earlier.  The problem is the the weather and my schedule hasn't align very well lately and when I did fly it was low level. The previously problem was about 15 years or so once that I realize the problem.  Here is the scenario, when I climbed above about 2500 agl then the problem stuck out to me like a sore thumb, the Manifold pressure gauge act like an altimeter. As it turns out the manifold pressure line had leak and my brother had help me fix it.   it could have been an ether a manifold pressure line leak or defective MP gauge. But I couldn't remember how we trouble shot the  problem. When I had  tried to fix the problem first time I was using vacuum  hose with a reducer but the vacuum motors are way to noisy think I had tried can air whatever reason it didn't work at the time. My brother had reminded me that we had probably used a 200ML syringe to trouble shot the problem.  With all new electronics added (CGR Engine monitor and SureFly Mag) I didn't want find out effect that the syringe might have on them. So I removed them from the circuit put this time I use a 500ML syringe  while examining aluminum manifold pressure line it work harden on me and  broke. So I ether had a piece of debris in the line or another line manifold aluminum leak.  I rebuilt the aluminum manifold pressure line and I got to fly today and it worked great.

Is there a company out there that make -2 hose for manifold pressure lines?  instead of  Aluminum -2 manifold pressure line. Most Hydraulic hoses go down to -3  that I have found. 

 

Thanks,

James '67C

[carusoam]

James,

Are we talking about the 1/8” aluminum tube for the MP gauge?

Briefly…

My 65C broke that line… at the weep hole…

Replacing it is easy… finding the weep hole dimension is a bit of a challenge…

Its in a Mooney drawing not for the M20C…

 

The calibrated weep hole needs to be there for the MP gauge to read correctly…

Best regards,

-a-

[47U]

15 minutes ago, jamesm said:

s there a company out there that make -2 hose for manifold pressure lines?

Precision Hose Technologies makes -2 hose assemblies.

https://www.aircrafthose.com/

Aircraft Spruce sells -2 AN hose fittings and hose.  Your A&P/IA might be willing to make a hose up for you.  

You should research to find out if the calibrated weep hole -a- references is applicable to your model/serial number. 

[jamesm]

If I am not mistaken on my setup '67C the weap hole is on the  engine side on the after the adapter/coupler or in the adapter itself as it goes into the  #3 cylinder prime port. I think might be  3/8" that gets reduced to 1/8" line then goes into  firewall. It sure  would be  nice if EI made a manifold pressure  transducer  that could be mounted in the  engine side of firewall. One less box on firewall cockpit area to find room  for.

I will have to check  that out  thanks.

James

 

[carusoam]

The weep hole referenced…

is resident in the 1/8” soft aluminum tube, attached to the back of the MP gauge on the panel… it is about two inches from the instrument itself…

The hole allows air to be drawn into the cylinder at the other end… flushing out any blue goo that may have crept towards the MP gauge after shut down…

Best regards,

-a-

[47U]

On 3/22/2022 at 8:10 PM, carusoam said:

Replacing it is easy… finding the weep hole dimension is a bit of a challenge…

See archive screen shot below… thanks -a-!

I replaced my MP aluminum line from the firewall to the gauge after the line was broken during some panel work.  I didn’t notice any weep hole… maybe the line was not original.  I guess I need to order me up a .023” drill bit.

My question is, what affect does the weep hole have on MP gauge reading?  Is insignificant?  Or, is calibration of the MP pressure gauge compensated for a small amount of air entering through the weep hole, therefore slightly lowering the MP reading at the gauge.  If the gauge is in fact compensated, and I’m setting MP without the weep hole, aren’t I indicating a higher MP than I would be if I had the weep hole, i.e., I’m running less power than I think I am as indicated on the MP gauge?

No wonder I’m slower than my Mooney friends…   

 

[carusoam]

22 hours ago, 47U said:

See archive screen shot below… thanks -a-!

I replaced my MP aluminum line from the firewall to the gauge after the line was broken during some panel work.  I didn’t notice any weep hole… maybe the line was not original.  I guess I need to order me up a .023” drill bit.

My question is, what affect does the weep hole have on MP gauge reading?  Is insignificant?  Or, is calibration of the MP pressure gauge compensated for a small amount of air entering through the weep hole, therefore slightly lowering the MP reading at the gauge.  If the gauge is in fact compensated, and I’m setting MP without the weep hole, aren’t I indicating a higher MP than I would be if I had the weep hole, i.e., I’m running less power than I think I am as indicated on the MP gauge?

No wonder I’m slower than my Mooney friends…   

 

Wow!

Look at that!

I looked up my hand written notes of a phone call I had with Mr. Bill Wheat!

 

Without the weep hole… the error is a variable range, with the most error with the throttle pulled back… least, when pushed all in…

The needle goes off scale… at idle…

It also sets you up for the failure the weep hole is intended to prevent… sucking fuel into your gauge… after shutdown…

The LL is a sticky substance…that would collect easily on the fine inner workings of a mechanical gauge…

 

If you can…. Go back to the broken line bits…

You will find the remnants of the weep hole right in the middle of the break! 

 

For its replacement… support the aluminum line properly…  it’s wobbling around willy nilly… tries to work harden the hole… and then a crack initiates, propagates, and waits for the hap hazard hand to come along and bump it…

Essentially the line cracks open where the weep hole used to be… thus hiding the actual hole to the casual onlooker…

Its tiny, and it’s half a hole….

 

Bill Wheat was a special person… great mechanical engineer, customer service engineer when he needed to be…

I think he was also know as Mr. Terrible?  See if @MooneyMitch can confirm that…   
 

Good luck with centering the small drill on the piece of tubing… there is probably a whole special procedure to do it the best way…

Great memories found!

Go MS!

Best regards,

-a-

 

[jamesm]

II know this  question  has probably been asked about  weep hole. I know that  I have replaced  aluminum  manifold pressure line from firewall to  mechanical manifold pressure instrument. At least a couple times and never put the weep hole in line the mechanical manifold pressure gage line. It works  fine.  I now have EI CGR30 engine monitor It seems  works  fine  best to my knowledge. It's  has been 3 years or so. Is it necessary in digital manifold pressure transducer setup to have a weep hole?

James

[carusoam]

9 hours ago, jamesm said:

II know this  question  has probably been asked about  weep hole. I know that  I have replaced  aluminum  manifold pressure line from firewall to  mechanical manifold pressure instrument. At least a couple times and never put the weep hole in line the mechanical manifold pressure gage line. It works  fine.  I now have EI CGR30 engine monitor It seems  works  fine  best to my knowledge. It's  has been 3 years or so. Is it necessary in digital manifold pressure transducer setup to have a weep hole?

James

The weep hole is for the mechanical gauges…. To protect their innards… their face is calibrated to work with the hole…

 

Good news….

none of the weep hole technology applies to a digital instrument… 

Fly on!

-a-

[MooneyMitch]

On 3/24/2022 at 10:47 PM, carusoam said:

I think he was also know as Mr. Terrible?  See if @MooneyMitch can confirm that…   

Every time I asked Bill how he was doin'?  His immediately reply was "terrible" !   Such a great treasure was Mr. Bill Wheat.