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issues with Fuel Servo


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Last august/September I changed out my engine with a genuine Lycomming rebuilt engine.  It came with a new fuel system including a new servo.

I have flown the plane for approximately 85 tach hours and when the throttle was pulled all the way back, the servo was stuck hard and took a good deal of effort to push open...

Called Airpower (agent that sold us the engine)  they told me to remove the servo and send it to Avstar in Florida....I next day'd it out...will see how quickly I get it back.  The woman from Avstar told me to label the paperwork AOG....aircraft on ground!....their terminology for RUSH!

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AOG is a universal term...

It gets used on MS sort of often... well, we don’t brake down that often...

But, when we do... AOG in the title gets some responses pretty quickly.

 

Larry, were you able to check if it wasn’t the control cable first?

Nothing scarier than stuck controls...

PP thoughts only...

Best regards,

-a-

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very good question....cable is completely smooth (when unattached)  you can operate the throttle lever with one hand but it takes a lot of effort...likely about 20 inch pounds to get it to come off of dead closed...

While I never felt this to actually be unsafe, its creates excessive cable tension, and likely wear...and could cause cable failure especially if the tension required kept getting harder.

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I had never adjusted the idle setting....when running at idle it would be at about 850, and when you lean out, you could get it up to 950 rpm

My six month old servo went out Monday afternoon to florida to AVSTAR...they sent it back next day air and I have it back this morning....smooth as silk in the operation.

It looks like they did a complete overhaul...it is painted a different color of gray, and all of the safety wires have been completely redone.  They didn't tell me what was wrong, but they said it was definitely a warranty issue....hopefully will get it reinstalled today

 

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On 5/7/2019 at 4:57 AM, larrynimmo said:

very good question....cable is completely smooth (when unattached)  you can operate the throttle lever with one hand but it takes a lot of effort...likely about 20 inch pounds to get it to come off of dead closed...

While I never felt this to actually be unsafe, its creates excessive cable tension, and likely wear...and could cause cable failure especially if the tension required kept getting harder.

Do you have the throttle quadrant?  There is a tension adjustment on the co pilot side.

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On 5/7/2019 at 5:43 AM, M20Doc said:

Is the throttle plate sticking in the bore because the idle stop screw is backed out too far?

Clarence

It is amazing how little the idle screw needs adjusting to make big changes in RPMs

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2 hours ago, larrynimmo said:

I had never adjusted the idle setting....when running at idle it would be at about 850, and when you lean out, you could get it up to 950 rpm

My six month old servo went out Monday afternoon to florida to AVSTAR...they sent it back next day air and I have it back this morning....smooth as silk in the operation.

It looks like they did a complete overhaul...it is painted a different color of gray, and all of the safety wires have been completely redone.  They didn't tell me what was wrong, but they said it was definitely a warranty issue....hopefully will get it reinstalled today

 

850 RPM idle speed and +100 RPM is too fast and too rich.

Clarence

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1 hour ago, M20Doc said:

850 RPM idle speed and +100 RPM is too fast and too rich.

Clarence

Yep.   they will start loping around 500.   650-750 is per the instructions with a 50 rpm rise when shutting off from full rich.

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6 hours ago, M20Doc said:

850 RPM idle speed and +100 RPM is too fast and too rich.

Clarence

This is how you get those loooooong floaty landings.     850 rpm static idle is still making significant thrust and it'll drag you way on down the runway when you're trying to land.   It really needs to be down around 650 rpm (spec) for this reason.

When I had my original engine instruments the aluminum line for the manifold pressure gauge broke near the cylinder.   That made enough of a vacuum leak to add 100 rpm or so to the idle.   That made a very noticeable difference when trying to land.   Keeping idle at spec makes a difference.

 

 

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With my A&P mechanic, we installed the new servo (took us about 2 hours)...and what a difference....there must of been issues with the original one from the beginning.  First of all, there was no resistance in operation...set landing gear warning switch...all smooth as silk....original one was never that smooth.

with the new servo, engine would run great at a 650RPM idle.  never could run it that slow before.  To get my engine to idle decently, I had to lean it out on idle more than half the way out.  now there is very little difference at idle when I pull it out and the fuel flow was steady at about 1.3 gph while idling....Whenever I used to do the runnup I used to get a little bit of a hiccup when shutting down the right mag...never on left mag.  Today there was no hiccup at all.  The climb out and cruise seemed to be identical to the operation of the 6 month old servo.

I am grateful to the staff of AVSTAR who truly expedited my rebuild and they shipped it back next day air...all at no charge...and Lycomming will pay for the removal, reinstall and shipping...Its nice when a warranty actually means something.  I shipped it out Monday afternoon and I flew the plane on Thursday afternoon.  I will always remember "AOG"

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