Fuel Return Lines?

Hi Mike,

Page 6, section 73-00-00 in the Edition 2/Rev 1, February 2015 installation manual for the carbureted 912 series engines, available for free download at the Rotax website, states the return line is required, and in a diagram, depicts the return line, with a restrictor of specified size, routing from the fuel distribution manifold to a fuel tank. Below is a copy and paste:

“The installation of a fuel return line is mandatory. If the fuel distributor piece with regulator from ROTAX is not available, the fuel pressure must be regulated by a restriction in the fuel return line, which ensures that the fuel pressure is under all operating conditions within the operating limits specified by ROTAX.”

Jim

Thanks Jim.  I now have to speak to the kit manufacturer about this as the 912 ULS does NOT have a return line TO THE TANK.  I'll update this thread when I get a reply from RANS.

Michael Tucker wrote:

Hi Bill, thanks very much for your reply.  Is your comment about returning the fuel line to the gascolator for the 912 ULS or the 912 iS (or both)?  My RANS S19 kit uses the 912 ULS and the return fuel line goes to the gascolator.

Mike

It is a bad idea for the ULS, but vapor bubbles in the fuel line get vented out in the Carb float bowl, often without much notice.

In the Fuel Injected versions, the vapor bubbles that exit through the injectors cause misfires.

The bubbles that continue on to the pressure regulator get returned to the gascolator for another shot at the injectors.

There is only one way out and it does not go without notice.