Fuel flow problems

I purchased both Andair fuel boost pump and fuel valve one year ago and installed them on my RV-7A while building.
Two months ago started the engine for the first time and it ran well at idle and up to 1800 RPM. I ran the engine for approximately for 5 mins to allow the oil to warm up before increasing the power to 1800 RPM.
Last month I started the engine for the second time but it was not getting enough fuel and was sputtering (had 5 gallons of fuel in the tank). During the second engine run up the mechanical fuel pump could not provide enough fuel and the problem remained the same even when assisted by the fuel boost pump.
The aircraft was pushed back in the hangar and I disconnected the fuel hose from the Fuel Servo in order to check how much flow I was getting. I was getting only 12 gallons per hour out of the fuel flow gauge and also timed the flow and calculated the result which was the same. After checking for the obvious (blockage,vent blockage) I found no blockage. I proceeded to remove the fuel pump from the floor and connected a hose from the tank to the fuel boost pump I managed to get a output of 45 gallons per hour. I reconnected the hardware back to where it was originally and turned the boost pump back on and got 45 gallons per hour.
I never found any blockage or anything else for that matter. I don't know what the problem was and now for some reasons it works. I am getting ready to fly the airplane but now I am concerned about the fuel system (boost pump or fuel selector).


Any recommendations

Proceed carefully Bob ( it sounds like you are) - this is why we do fuel flow tests before flight - because if there is a blockage, it usually occurs when you are just past the point of no return on your first take-off. SOMETHING caused your initial problem, and things that fix themselves have a nasty tendency to come "unfixed" at the worst time.

I wouldn't want to make the first flight with an unexplained anomaly in the fuel system still on the books.

Check your hoses for a "flap" of rubber that might have gotten carved up when the assemblies were made.

Fuel valve...?? Ice... ??

Bob, sounds like good testing. Did the fuel selector valve position change? Did you see the same results from both tanks? Any possibility that the selector valve was between detents? How cold was the ambient temp? Ice slug in fuel line?
- Roger

It seems like the restriction might have been before the (upstream) boost pump since the engine driven fuel pump was also unable to deliver the right amount of flow. I was getting the same result from both tank so I switched the fuel selector to the respective tank. I will check my flexible fuel hoses for obstructions which are downstream of my fuel boost pump.

I have two fuel filters, one in each wing root right after the output from the tank and before it goes back in the airplane. I did not like having only one fuel filter just prior the boost pump, like Van's plan call for, so with two filters in the wing root which is easier to clean during inspection and less messy and also the fact that I have some redundancy should the fuel be contaminated I can switch tank and look for a place to land.

It sounds like the fuel path is this:

1. pick up in tank (line to fuel filter) -> 2. fuel filter (line to selector) ->3. Andair selector (line to boost pump) -> 4. Boost pump (line to fuel sensor) -> 5. fuel sensor (line/hose through firewall to engine pump) -> 6. engine pump (mechanically actuated diaphragm pump) (hose to servo) -> 7. Servo

A. In the beginning, 12 GPM at #7

#3 boost = on
#6 mech = on, engine spinning

B. 12 GPM @ #7

#3 - boost = on
#6 mech = off - engine not running

C. Removed #3 (boost pump), installed hose from tank to boost pump (bypassing installed line - and filter?)
= 45 gpm

D. Like A, but yields 45 GPM

Is the above correct?

If so, it sounds like some where the obstruction, or air bubble, or leaking fitting, has been purged, fixed, and the system is operating as designed.

My guess, is a suction leak at the boost pump inlet.

If this is the case, you have dissembled the system, retested and it works properly. You might check it again, then declare it done. I know you want to find something definitive that was amiss, but if it was a loose fitting or one that did not seal well, then, there is no way to go back and prove it - unless you loosened one to satisfy yourself that it was possible. The flow should be checked with the flow valve in both positions to be sure it did not participate in the issue.

This is all I have, and what is listed deserves some thought and comment for validity.

Thank you everyone for your inputs I realy appreciate

I spoke with Andair and they suspect a leaky connection introducing air in the system or an air bubble. The problem went away during our trouble shooting after we eliminated the air in the system.
Once thanks again for everyone's input

I found few B nuts not completely tight which was the cause of air intrusion. Problem solved...