diagram of a fuel servo

[Robert M. Gary]

My fuel servo is coming back from the shop. I wish I better understood
how they work. One day my plane just stated running so rich that I
could almost not keep the engine runnnig. I was pulling about 7GPH at
1500 (normal is about 3). However, if I shutdown and restarted it would
run correctly about 10% of the time.
So the fuel shop received it and noticed the FF was too high. They
replaced a spring and got the flows in line. However, now I'm worried
that they fixed the 90% case and not the 10% case (which was normal).
If they replaced a spring with a lighter spring, how would that solve
the issue? Why did this happen all of the sudden? Why isn't it
consistant? My plane has been down for 3 weeks now and I fear I'll get
the unit back and it won't work and I'll be down even longer (with a
full FF overhaul). The fuel servo has 900 SFNEW.

Is there an on-line diagram of a fuel servo? I'd like to better
understand how the springs, diaphrams, etc work. I'm told there are
only a few moving parts, but not sure what they are.

-Robert, M20F

[Jim Macklin]

Google for "Bendix fuel flow divider" and you'll find pages
such as
http://www.dgsupply.com/trouble.html and especially
http://www.precisionairmotive.com/rsasupport.htm

For a full description get FAA AC 65-12A, which is on-line.
Chapter 3 has what you want.




"Robert M. Gary" > wrote in message
oups.com...
| My fuel servo is coming back from the shop. I wish I
better understood
| how they work. One day my plane just stated running so
rich that I
| could almost not keep the engine runnnig. I was pulling
about 7GPH at
| 1500 (normal is about 3). However, if I shutdown and
restarted it would
| run correctly about 10% of the time.
| So the fuel shop received it and noticed the FF was too
high. They
| replaced a spring and got the flows in line. However, now
I'm worried
| that they fixed the 90% case and not the 10% case (which
was normal).
| If they replaced a spring with a lighter spring, how would
that solve
| the issue? Why did this happen all of the sudden? Why
isn't it
| consistant? My plane has been down for 3 weeks now and I
fear I'll get
| the unit back and it won't work and I'll be down even
longer (with a
| full FF overhaul). The fuel servo has 900 SFNEW.
|
| Is there an on-line diagram of a fuel servo? I'd like to
better
| understand how the springs, diaphrams, etc work. I'm told
there are
| only a few moving parts, but not sure what they are.
|
| -Robert, M20F
|

[Robert M. Gary]

Jim Macklin wrote:
> Google for "Bendix fuel flow divider" and you'll find pages
> such as
> http://www.dgsupply.com/trouble.html and especially
> http://www.precisionairmotive.com/rsasupport.htm
>
> For a full description get FAA AC 65-12A, which is on-line.
> Chapter 3 has what you want.

I didn't see a diagram of the servo in the above link. I found the AC
(which was very interesting) but it seemed to only talk about carbs.

-Robert

[Jim Macklin]

It talks about all types of systems, scroll further.




"Robert M. Gary" > wrote in message
oups.com...
|
| Jim Macklin wrote:
| > Google for "Bendix fuel flow divider" and you'll find
pages
| > such as
| > http://www.dgsupply.com/trouble.html and especially
| > http://www.precisionairmotive.com/rsasupport.htm
| >
| > For a full description get FAA AC 65-12A, which is
on-line.
| > Chapter 3 has what you want.
|
| I didn't see a diagram of the servo in the above link. I
found the AC
| (which was very interesting) but it seemed to only talk
about carbs.
|
| -Robert
|

[Robert M. Gary]

Jim Macklin wrote:
> It talks about all types of systems, scroll further.
>
Cool, thanks! It looks like all the movable parts are part of the
spring. I guess its possible the spring was hanging up or something.
The shop said the mixture control is a moving part but that its a very
simple ball that turns and doesn't cause problems. I'll cross my
fingers that its fixed. If so, I got of easy. $160 plus R&R. If not,
I'll be looking at $1500 plus R&R.

-Robert

[Jim Macklin]

Glad to help. The FAA manuals, 65-9, 65-12, and 65-15 are
on-line as is 43-13. You can also find a lot of
manufactures stuff if you search well and pick the proper
terms.



"Robert M. Gary" > wrote in message
oups.com...
|
| Jim Macklin wrote:
| > It talks about all types of systems, scroll further.
| >
| Cool, thanks! It looks like all the movable parts are part
of the
| spring. I guess its possible the spring was hanging up or
something.
| The shop said the mixture control is a moving part but
that its a very
| simple ball that turns and doesn't cause problems. I'll
cross my
| fingers that its fixed. If so, I got of easy. $160 plus
R&R. If not,
| I'll be looking at $1500 plus R&R.
|
| -Robert
|