Throttle Body Restriction???

[Steve A]

I have esssentially completed my plane and am testing the fuel system. I run fuel through the electric fuel pump
through the fire wall to the fuel pump and get 50 gallons per hour flow as measured with my Grand Rapids EIS. I
confirm this flow as it fills a 5 gallon plastic fuel tank in a few minutes. Now when I hook the fuel hoses up to my throttle
body, I just get fuel barely leaking through. Initially I hooked up aluminum tubing to the hose coming up through the engine
and connecting at the fuel injection spider. When I hook the aluminum tubing to the connection at the bottom of the
throttle body, I get the same low fuel flow. THerefore the obtruction is definitely at the throttle body.

I purchased a Lycoming IO 360 from Van's with horizontal induction system. It appears to me that the throttle
has an obstruction. I am opening the mixture to full open as well as the throttle to full power. A friend has a angle valve
IO 360 and tells me that there is a screen in the throttle but I have not seen one.

Any ideas on how to get the fuel flow to a normal pressure would be appreciated.

Thanks.

Steve Anderson
RV 7A Lafayette, La.

[John Clark]

Yes, you are going to have a restriction at the throttle body, that is how the system regulates the fuel.

RSA fuel injection systems are mass-air flow type fuel injection systems. In other words, the throttle body servo senses the amount of air moving past the throttle by use of a venturi. A diaphragm in the servo regulates the amount of fuel supplied to the flow divider (manifold, fuel spider) by comparing the air pressure from the venturi. Next, the flow divider divides the steady stream of fuel into smaller streams of fuel, one for each cylinder.

John Clark
RV8 N18U "Sunshine"
KSBA

[David-aviator]

Originally Posted by Steve A

I have esssentially completed my plane and am testing the fuel system. I run fuel through the electric fuel pump
through the fire wall to the fuel pump and get 50 gallons per hour flow as measured with my Grand Rapids EIS. I
confirm this flow as it fills a 5 gallon plastic fuel tank in a few minutes. Now when I hook the fuel hoses up to my throttle
body, I just get fuel barely leaking through. Initially I hooked up aluminum tubing to the hose coming up through the engine
and connecting at the fuel injection spider. When I hook the aluminum tubing to the connection at the bottom of the
throttle body, I get the same low fuel flow. THerefore the obtruction is definitely at the throttle body.

I purchased a Lycoming IO 360 from Van's with horizontal induction system. It appears to me that the throttle
has an obstruction. I am opening the mixture to full open as well as the throttle to full power. A friend has a angle valve
IO 360 and tells me that there is a screen in the throttle but I have not seen one.

Any ideas on how to get the fuel flow to a normal pressure would be appreciated.

Thanks.

Steve Anderson
RV 7A Lafayette, La.

With engine static, not running, mixture full rich, fuel flow through the controller is about 1 gph with the throttle closed and a little more wide open. What you see is perfectly normal. As John says, it takes air flow through the controller to get more fuel moving.