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Bit of a long shot, but your original pump was higher pressure than specified by Jabiru. According to the installation manual, pressure should be in the range 0.75 psi to 3 psi. The pump you have fitted now is the correct range but you may need to check that the pump really is pumping the correct pressure. A simple ground check would be to disconnect the carburetor vent tube, the little tube that runs from the carb to the air cleaner box, and then run the pump. If the pressure is too high and forcing the float valve off its seat, I think you should get fuel coming out that vent, indicating that the float bowl is over full.

Peter

Did not know about that for a check. I will try that. Thanks

If the engine idles fine with the boost pump off then I would feel pretty sure that the boost pump is pushing too much pressure / fuel quantity which will override the carby's float bowl shutoff and basically flood the engine with fuel. If the engine runs OK at higher RPM settings with the boost pump on then that will likely verify that the boost pump is pushing too much pressure to the carby. Also don't forget that the gravity head pressure is still there especially with a full tank. A flow regulator valve can be installed in the fuel line to limit fuel flow but it is another mechanical device that can fail and put you in a bind. If I had a boost pump in my Sonex I would treat it as a emergency device to save the day only when the engine drive pump fails.

MHO and your mileage may vary!

sport65 wrote:I have a problem with my engine loosing rpm to the point of failing with the standby fuel pump turned on (on the ground at idle). I have replaced the standby fuel pump with two different units. I used the facet 3.5 to 4.5 psi pump first (recommended by Jabiru). Changed that to a 1.5 to 2.5psi facet that had a one way check valve(only one available at correct psi from facet). I thought the check valve might be the problem, so replaced with a holley 1.5 to 2.5psi with no check valve. Same problem. The engine runs fine above idle with the standby pump on. Idles fine with the standby pump off. Engine failed on rollout with standby pump on. I have the fuel bowl level set at 10.5mm. I did that with the aircraft in a level attitude( I'm a taildragger ). I'm going to set the fuel bowl level to 12mm, but don't think that is really the issue. Any one familiar with this issue ?

Any chance you have part numbers for those pumps, specifically the Facet with the check valve? I suspect after reading this that I purchased the wrong pump.

The one with the check valve is 40163. 40105 was the 3.0 to 4.5 psi jabiru usa said use. I think it works on the Jabiru aircraft do to the length of fuel line and pressure loss since the pump is behind the baggage compartment. My pump has only about three feet of fuel line to the carb. I have not found the issue yet and the Jabiru forum did not say the check valve in the pump was for sure a problem, I just replaced it since they did not rule it out. Replacing it with one without the check valve did not make the problem go away.
I did the test to see if the pump pushed fuel up the balance tube, it does not. I lowered the fuel bowl level to 12mm, but have not run it yet. Can someone say for sure that the carb should be level when setting the fuel bowl level. I just want to make sure of everything I'm doing. I am using a t fitting with a pressure guage to verify fuel pressure Thanks for the ideas!

Well finally seem to have fixed it. Ran the engine and no more engine stalling with the stby fuel pump on. The only change made was lowering the float level to 12mm (from 10.5mm). Apparently that was the problem. I don't know why, I was told the float has an acceptable range that I was within. Maybe its a taildragger thing that the range is more limited. I don't know, but hope this helps someone else in the future if they encounter this issue. I will update if it comes back. Thanks to everyone for the ideas and help!!!

Thanks for the update!! I have a Gen 4 3300 with a Bing. Good info.


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Glad you got that resolved. Suspect you are right about it being a tail dragger thing. Now that you mention it, had an old garden tractor that did not like hills for same reason, fixed same way.

David A.

No hills where I live or might have figured that out sooner :)