Higher pressure electric fuel pump cause carb leak?

[Piper J3]

The carburetor float bowl (especially on Rotax 9-series) is a very violent place. The carbs are located at the extreme from engine centerline and are thus subject to large fluctuations in vibration. Couple that with turbulence in flight and you can visualize fuel slushing every direction within the float bowl. Difficult to control fuel level….

Best practice is to use lightest floats in conjunction with clean needle and seat – both with minimal wear. Use magnification with good lighting to inspect needle and seat. Also check and verify fuel level is correct height in bowl per spec. In addition, check float pivot hardware for wear and replace if necessary…

[RFSchaller]

Totally different setup, but I put a normal and emergency fuel pump on my first home built (a WAR FW-190). I had both operating during takeoff. The engine ran rough, and I had to use lean mixture during takeoff to smooth it out until I finally figured it out. The engine was happy with the pressure of gravity feed from the tank mounted only a foot above the carburetor.