Should this engine have a fuel return line?

QUESTION: I have a Glasair, started by someone else, with an IO-320 engine. He has a fuel return line from the side of the throttle body going back to the bottom of the header tank. It is my understanding that there is not supposed to be a fuel return line on this system.

I can’t find anyone who seems to know for sure. Help!

Jack Huston
Camp Verde, Ariz.

ANSWER: Jack, thanks for your question. I’ve got some things for you to check, including the data plate on the fuel metering device. Look for the model of the unit.

All of the fuel control units used on the Lycoming IO-320 series, to my knowledge, utilized the RSA system. None of the RSA systems require or use a “”return to tank”” line. The RS system does use that configuration, but I have never known any of those to be used on an IO-320.

One unique thing that does come to mind, when I think of the IO-320 series used on the PA-30 Piper Twin Comanche, is the fact that the right engine throttle body did have a port coming off the top of the unit that served as a fuel source for the cabin heater.

I hope this information will allow your project to continue with one less question.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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