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Silver Hawk Dumping Fuel into Air Filter Below

jherzog

jherzog

Member
Hello,

I have an RV-9A that I bought last year. It has an O-320 with a Silver Hawk fuel injection system. Towards the end of last year, I started to notice a little bit of fuel under the cowl, at the top of the nose wheel fairing, after most flights. On further inspection, I saw that the air filter below the Silver Hawk was becoming saturated with fuel. More recently, the engine has begun sputtering when the engine is run at RPMs below 1,000. Seems to run fine at 1,000 RPM and above.

Has anyone else experienced this with their Silver Hawk, or have any tips on troubleshooting?

Thanks in advance,

Jordan
 
jherzog said:
Hello,

I have an RV-9A that I bought last year. It has an O-320 with a Silver Hawk fuel injection system. Towards the end of last year, I started to notice a little bit of fuel under the cowl, at the top of the nose wheel fairing, after most flights. On further inspection, I saw that the air filter below the Silver Hawk was becoming saturated with fuel. More recently, the engine has begun sputtering when the engine is run at RPMs below 1,000. Seems to run fine at 1,000 RPM and above.

Has anyone else experienced this with their Silver Hawk, or have any tips on troubleshooting?

Thanks in advance,

Jordan
Click to expand...
I suggest you call AirflowPerformance
airflowperformance.com

CONTACT - AIRFLOW PERFORMANCE

Airflow Performance, LLC 111 Air Flow Drive Spartanburg SC 29306 864-576-4512 864-576-0201(Fax) [email protected] [email protected] [email protected] [email protected] CONTACT US For Driving Directions Click Logo For Flying Info Click Logo
airflowperformance.com

Good luck
 
Assuming nothing obvious like a loose fitting on the servo, the likely culprit is a failing seal inside the servo.
I second the recommendation above.
Also... Ground the plane.
 
Been there, done that!

How many hours do you have on this fuel servo? is it still under warrantee? I'm assuming that you have looked for the obvious loose fuel lines. Is the servo leaking fuel at the fuel inlet? If so, there are two "O" rings that probably need to be replaced.
When you shut down the engine are you pulling the mixture control to shut off the fuel? With the airbox removed and the fuel pressure at aux pump MAX, does the servo leak fuel? If so, it needs to be rebuilt by AirflowPerformance.....

There are documents on the Airflow Performance web site for doing leakage tests on this fuel servo....
 
Jordan

check that the air box has 2 fuel drain holes to drain both inside and outside of the filter. both these holes should then go into the hose and drain to the firewal.

regards Peter
 
kiwipete said:
Jordan

check that the air box has 2 fuel drain holes to drain both inside and outside of the filter. both these holes should then go into the hose and drain to the firewal.

regards Peter
Click to expand...
Peter,
Thank you. I definitely do not have any fuel drain hoses for my air box -- photo below. Where would the drain ultimately go?
RV9A Airbox.jpg
Jordan
 
Fred.Stucklen said:
Been there, done that!

How many hours do you have on this fuel servo? is it still under warrantee? I'm assuming that you have looked for the obvious loose fuel lines. Is the servo leaking fuel at the fuel inlet? If so, there are two "O" rings that probably need to be replaced.
When you shut down the engine are you pulling the mixture control to shut off the fuel? With the airbox removed and the fuel pressure at aux pump MAX, does the servo leak fuel? If so, it needs to be rebuilt by AirflowPerformance.....

There are documents on the Airflow Performance web site for doing leakage tests on this fuel servo....
Click to expand...
Thanks Fred. The unit is about 15 years old -- definitely out of warranty, and probably due for service based on age, if not hours (which are low). Yes, I always pull the mixture to stop the engine at shutdown. I will run a test and see if fuel leaks down from the servo with the fuel boost pump on. My suspicions is the fuel is coming out one or more venturi tubes, but we will see.
 
jherzog said:
Peter,
Thank you. I definitely do not have any fuel drain hoses for my air box -- photo below. Where would the drain ultimately go?

Jordan
Click to expand...
HOLES not HOSES.
There should be two small holes, one in the rear, bottom, outside the air filter. Second one on the bottom inside the filter. Unless you have an ALT AIR door down there, in which case any gas dribbles will leak out the door.
 
blaplante said:
HOLES not HOSES.
There should be two small holes, one in the rear, bottom, outside the air filter. Second one on the bottom inside the filter. Unless you have an ALT AIR door down there, in which case any gas dribbles will leak out the door.
Click to expand...
Understood Peter. You say both of these holes "should then go into the hose and drain to the firewall". I have no such hose right now. Does yours exit the bottom cowl at the firewall?
 
I only have holes, no hoses.
When I built my airbox it called for these holes, and didn't mention any hoses.
Maybe that's a change since 8 years ago...
-Bryan
 
jherzog said:
Thanks Fred. The unit is about 15 years old -- definitely out of warranty, and probably due for service based on age, if not hours (which are low). Yes, I always pull the mixture to stop the engine at shutdown. I will run a test and see if fuel leaks down from the servo with the fuel boost pump on. My suspicions is the fuel is coming out one or more venturi tubes, but we will see.
Click to expand...
I stand corrected on the fuel servo source! Precision is correct. See the attached trouble shooting guide. Hope it helps..
 

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Fred.Stucklen said:
I stand corrected on the fuel servo source! Precision is correct. See the attached trouble shooting guide. Hope it helps..
Click to expand...
Thanks Fred,
This manual says it is for RSA family of servos. Is it also applicable to the Silver Hawk?
It says that with the fuel outlet capped, throttle full open, mixture full rich, and boost pump on for 3 minutes, at most a drop should come out the air inlet port at the bottom of the servo.
 
jherzog said:
Thanks Fred,
This manual says it is for RSA family of servos. Is it also applicable to the Silver Hawk?
It says that with the fuel outlet capped, throttle full open, mixture full rich, and boost pump on for 3 minutes, at most a drop should come out the air inlet port at the bottom of the servo.
Click to expand...
The manual covers Silver Hawk servos...
 
The RSA line are for certified aircraft, the Silver Hawk are essentially the same but are for experimental aircraft.
 
Just to add to the above I made 2 holes one as shown inside the filter and one outside. So if I fly in heavy rain that it can’t pool in the back of the airbox.
 
Fascinating! The plan clearly shows an alt air door, and a drain hole and hose! I want someone to test the liquid tightness of that alt air door on a current build. Every one I've ever seen would leak liquid at least as fast as a #19 hole. Belt and Suspenders?
 
blaplante said:
Fascinating! The plan clearly shows an alt air door, and a drain hole and hose! I want someone to test the liquid tightness of that alt air door on a current build. Every one I've ever seen would leak liquid at least as fast as a #19 hole. Belt and Suspenders?
Click to expand...
From memory the alt door fitting has a flange so might still leave some fuel in the bottom of the FAB, also any fuel that drained out would then be in the bottom of the cowl or down the gear leg which could be a fire risk. At least with the hose it can drain back clear of the cowl.
 
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