SonexBuilders.net

I have a 3300 with stock fuel pump and Bing carb. First flight in a couple of months, when spring arrives.

In the meantime, would it be wise to install an electric boost pump? What are others doing with similar
installations? Are the boost pumps in series or parallel with the mechanical pump, with check valves or
without?

Thanks for any input.

Rick

C-GRIX

Hi Rick

I am doing an engine swap to a Jabiru 3300 and kept the Bing carb. I put a Facet fuel pump in series with the mechanical pump and it has a check valve.

I have a low pressure facet pump in series with the mechanical pump, no check valves. Only ever use the facet pump as a backup.

Steve
Sonex 892 3300 jabiru 354 hrs

I did this when I had a rotec tbi... now I'm back on the Aerocarb I don't need it but it's still installed... I just don't use the fuel pump.



https://2.bp.blogspot.com/-Y6TjH7gTWt4/ ... 145051.jpg

I have a low pressure SU pump in series with the mechanical pump. It's rather heavy and bulky but does give a rather satisfying tick tick tick sound as it pumps up to pressure when it is first turned on so know you something is happening. It is just a back-up so I can turn it off after take off. It's a diaphragm pump so effectively incorporates a check valve.

Peter

I also have a Facet back up pump. With a Bing carb set up there is also a reasonable flow from gravity with the plane on its tailwheel and more then 15 litres of fuel in the tank.
On a side note I was servicing my plane last week, checking hoses etc and thought the hose was loose on the side of the mechanical pump. Further investigation I found the fitting in the fuel pump had come loose. I had to remove and dismantle the pump then I drilled and tapped the pump to accept a 1/8" npt fitting. There is a service bulletin out on just this fault.

I decided to install a Facet 4 psi boost pump between the gascolator and mechanical pump. Finished today
and turned it on to check for leaks, without the engine running. All the fuel lines are fine and the UMA pressure
sensor, which is T'ed in the line between the mech pump and carb read 2.9 PSI. Then I noticed fuel running out of
the air intake box. Upon closer inspection, the fuel was coming from the balance tube. Anyone know why I'm
getting fuel from the balance tube? I think it runs to the cavity around the diaphragm, shouldn't be fuel there.

Thanks for any suggestions.

Rick

I'd be checking the float level and needle and seat. With the engine level, allow the bowl to fill. Then shut off the fuel and remove the bowl. After removing the bowl, there should be about 12 mm from the lip on top of the bowl, to the fuel. To adjust bend the tab on the float that actuates the needle.

Carby adjustment in the maintenance manual page 63. https://jabiru.net.au/wp-content/upload ... 0002-7.pdf

The Jabiru installation manual states a minimum fuel delivery pressure of 0.75 psi and a maximum of 3 psi. The backup pump I've used for 9 years without any issues is also slightly higher than what Jabiru specifies. Its a facet 40105.

Fuel delivery section in the installation manual is page 27. https://jabiru.net.au/wp-content/upload ... 7_Inst.pdf

Hi Steve, thanks for the reply! I did take the bowl off. Its hard to get it off without spilling
fuel, but it seemed right full. I held the floats up with the pump on and it did stop the flow. I
tweeked the float to close the needle sooner and put the bowl back on, but still got
fuel from the balance tube when I tried the pump again.

My Facet is #40104, so max pressure is 4 psi. Do you have a pressure gauge? What pressure
do you see? I guess my next test is to start the engine and see if the mechanical pump also
causes the same problem. If so, the needle valve is faulty, or out of adjustment.

Rick

Hi Rick. Sorry I dont have a pressure gauge installed. If you just wind over the motor with the ignition off, the mechanical pump should fill the bowl in a few seconds. Then check to see if you the fuel is 12mm down from the lip of the bowl.

If you reckon its hard to not spill any fuel when removing the bowl, wait till you see how much fun getting the float assembly and needle back in can be. That little needle retainer clip is about as thick as a human hair and wants to fall off until the float pivot pin is back in place.
Cheers Steve