Higher pressure electric fuel pump cause carb leak?

[Charlie12]

My original electric fuel pump died, ES40105. Contact with Van's gave me the impression that I had no choice but to replace it with the 1.5 psi higher pressure ES40135, so I did (Van's no longer stocks ES40105). I installed it and immediately had the right carb overflow during pump testing. 861189 floats are not heavy despite 3+ years in service.

I had a certified Rotax technician inspect both carbs and replace floats, needle valves, and float bowl gaskets. He reinstalled the carbs today and during carb sync both carbs overflowed out the float bowl vents. Fuel pressure was around 7 psi, which is in the green in the revised range markings that go with the higher pressure pump. Clearly, my carbs will not tolerate the higher fuel pressure. Builder support suggested going back to the 40105 pump which is readily available, just not from Van's.

Has anyone else had similar experience and have insight into how to fix it?

[seagull]

I replaced my ES40105 fuel pump in March of 2021 with ES40135. Flight logs before and after the exchange show no increase in fuel pressure. My pressure runs average 5.1, under some conditions I have seen 6.0, but it has never caused a leak.

Looking back over logs before and after the pump was replaced I saw instances of a 6.0 pressure.

[Piper J3]

The reason for the higher pressure pump is related to vapor lock. You live in a part of the country with high seasonal temperatures and should adhere to Van’s good advice. I installed the new higher pressure pump on my RV-12 when I experienced vapor lock on takeoff several years ago. Not good… I have not had any problem with float level or fuel overflowing from the float bowl vent tube. I was running Bing floats (< 7 grams) but changed to Marvel Schebler epoxy floats shortly afterward. I would check float level setting and inspect float needle tip and seat for wear.

[bobnoffs]

if you must use that pump a pressure regulator will allow you to dial in whatever pressure you want. that is throwing another failure point into the mix and i am not suggesting you do this. rotax knows exactly how much pressure will overpower the float in the carb and i would think they could take care of this.
i had an internal fuel pump on an engine that would do this. the fix there was to replace the spring in the pump with a weaker one.

[PaulvS]

I'm aware of this occurring in another 912ULS non-RV12 installation. It was related to the fuel return line flow rate. This may/may not be relevant here, but I suggest checking that the restrictor port in the fuel return line is not blocked. Here's how:

https://vansairforce.net/community/s...d.php?t=183228

[bobg56]

I believe the fuel return line has a restriction orifice, make sure its not clogged.

[Charlie12]

I have checked the return line and it is not clogged. I was checking this immediately after installing the 40135 pump when I got the first overflow.

[seagull]

Since there are a lot of -12's that have changed to the 40135 pump with no issues, my guess is you got a defective or mis-marked pump.

[RFSchaller]

I wonder if there is seat damage on the float valve and it isn’t sealing properly.

[bobnoffs]

when i had the problem with the pump overpowering my bing carb i put a fuel pressure gauge in the line. either the carb is leaking before its rated pressure or the carb is being over pressured. one way to know.