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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 ?

It sounds more like a partial fuel blockage. Something to check:
* Remove the float bowl and check fuel flow into a container. I think you should get fuel flowing due to gravity even if the pumps are off. If the fuel flow is low, you just need to work your way back to find the blockage. If the fuel flows OK and then slows it would point to a blocked fuel tank vent.
* You shouldn't need to change the carb float level from standard.

Peter

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 that you are suffering from low electric power that is causing underpowered spark? If you are having this issue on an Aerovee and are using both ignitions, then you shouldn't have a spark issue if both systems are functioning properly. However, of your alternator is not producing current, then you are running off of battery only, and that can become an issue as you throttle up and draw more battery power through the two coils. It's worth a check it you haven't done so already.

Make sure there is no contamination on the float valve needle, or its seat, and that both are perfectly smooth. If questionable, replace the float needle. Also make sure choke is FULLY closed.

David A.

I have checked the fuel flow and replaced the filter. The fuel blockage does not quite seem to be it, because the engine will run fine at anything off idle(more fuel flow).
The engine is a Jabiru, so I have coils independent of the battery for spark. The pump would place a higher draw on the alternator, which would add some drag to the engine. I would think that would be an issue for all the Jabiru engines and aircraft, since they all have stby fuel pumps. In other words, what is making mine unique to cause this issue?
I have checked the float needle and I cant see or feel any contamination. I have not checked the choke though. I will check that.
Thanks for all the ideas guys! Any ideas are appreciated !!!

Hi Jeff, a little bit more information would help. Is this a new installation or a fault that has just appeared?

Full throttle on my 3300 uses about 40 litres/hour (nearly 11 gallons/hr) so you need a fuel flow of more than that. I think the aim is for pumps to be capable of 20 gallons/hour.

If it's an older engine, a hole in the carburetor diaphragm would cause a similar problem, but I have never seen that happen on a Bing carburetor, or for that matter on countless Mikuni and Keihin carburetors on motorcycles.

Peter

Just reread your original post. Are you saying that the problem is that the engine just isn't idling reliably?

Peter

Yes, it is not idling when I turn on the standby fuel pump. It will idle fine with the pump off.
The engine only has about three to four flight hours on it. I usually turn on the stby pump right before takeoff, so I was probably advancing the throttle and did not notice the issue. So I'm not sure if it always did it. I figured it out after it died on rollout.

What idle speed are you running??. Could it be to low and its just a coincidence its cut out out with the backup pump on.

Idle speed when it warms up is about 950-980. Still does not help with that high of an idle.