This doesn't seem right... video

Intuitively, something seems wrong with the linkage between the butterfly and fuel metering arm in my Precision Silver Hawk EX Fuel Injection. I suspect this may be something I'm just not understanding correctly.

As the throttle is opened to about 3/4, the linkage comes to center on the throttle arm and the fuel metering arm opens no further. As you move the butterfly to the WOT stop the linkage moves over center and the fuel metering arm moves to a slightly leaner position. This is how the unit came from the factory on my Aerosport IO-375.

Following is a link to a youtube video showing the linkage in motion. I refer to "mixture arm" in the video, I meant to say "fuel metering arm" (which is another assumption in itself). I'm hoping someone here knows a lot more about this than I do. Thanks! - Mark

http://www.youtube.com/watch?v=Ci5se-MuA7A

The lower arm needs to be repositioned lower?

Best call the company and confirm.

MTBengel said:

Intuitively, something seems wrong with the linkage between the butterfly and fuel metering arm in my Precision Silver Hawk EX Fuel Injection. I suspect this may be something I'm just not understanding correctly.

As the throttle is opened to about 3/4, the linkage comes to center on the throttle arm and the fuel metering arm opens no further. As you move the butterfly to the WOT stop the linkage moves over center and the fuel metering arm moves to a slightly leaner position. This is how the unit came from the factory on my Aerosport IO-375.

Following is a link to a youtube video showing the linkage in motion. I refer to mixture arm in the video, I meant to say "fuel metering arm" (which is another assumption in itself). I'm hoping someone here knows a lot more about this than I do. Thanks! - Mark

http://www.youtube.com/watch?v=Ci5se-MuA7A

Click to expand...

I just checked, mine does exactly the same thing. (same servo, IO360 straight from Vans/Lycoming) Although not worried about that since both shafts are pinned, I am curious about the practical information behind it. I will be watching for more . . .

My linkage was way off too

I had the same issue (IO360 stock from Vans) and posted on here for help with it. I think its just left in the position it is tested in. I had to cut out a cotter pin and reposition the levers so when they attached to my control cables they did what they were suppose to do.

Mark,
Mine is the same way. I have seen others (Certified) that do the same.
It comes that way from the OEM.

It flows fine at wide open throttle.

Lycoming tested my -M1B engine with this injector and even adjusted the idle during testing.

Set your throttle cable and build on with no concern about it.

Silver hawk Fuel Injection Servo throttle/Mixture arm

Okay Guys,

I am not an expert like Don Rivera who used to work for Bendix Fuel Injection before going "rogue" and forming Airflow Performance. I am sure he will see this and jump right on it in due time.

I too have a Precision Airmotive Silverhawk FI unit on my IO-360 swinging a Hartzel prop. Fine fuel metering unit and it's never missed a beat in the "millions" of dollars worth of blue juice it as metered.

On the throttle lever side of the unit there is that linkage that goes to the other smaller lever turning that shaft non linearly. That secondary shaft is not the primary mixture device. It is more of an idle mixture circuit adjustment. Thus the small thumb wheel that interfaces with that spring. Once you open up the throttle a certain amount (half throttle or more, NOT SURE), the idle mixture circuit in the fuel control is overridden or taken over by main metering circuits. Yes, we do have control of main mixture thus the mixture lever on the other side of the unit that goes from full rich to idle cut off (ico). That's going to be the extent of my explanation so as not to lose anybody. Lots of neat things go on inside of that fuel servo. It measures air flow and and then precisely meters the correct amount of fuel to match that airflow. That is why they are "flowed" on a bench with fancy instrumentation (big bucks). So......

The only adjustment you would make with that idle mixture adjustment thumb wheel is spelled out in the instruction/ops manual that comes with the Silverhawk. It's basically the 50 rpm drop test when you slowly retard your mixture lever towards idle cutoff. In theory, the rpm should rise about 50 rpm before rapidly dropping off during engine shutdown. It has to do with where your idle mixture should be set when engine is idling. I had mine too rich once and after landing at a 2500 foot elevation airfield at like 100 deg F, my engine would not completely shutdown with mixture pulled full cutoff. Hum, so I just turned the mags off and that did it. Okay, so let's see what Mr Rivera or any other Fuel injection gurus have to say.