Lycoming O-290

The EFS-3A is the recommended unit for the 0-290 engine. If your engine is an O-290-D then the throttle body will mount directly to the sump in place of the original Marvel Schebler MA-3 carb.

Many 0-290 engines are converted ground power units (GPU) and may have some differences that affect throttle body installation.  If your engine is a converted GPU, you will need to determine what oil sump has been installed on the engine.  If a proper O-290-D sump has been installed, an EFS-3A can be bolted directly to the bottom.  If a converted GPU has had the sump from the O-320 installed, the stud pattern will be too large for the EFS-3A requiring an adapter.

Some people with O-320 sumps have used the larger EFS-4, which will mount to the O-320 sump without modification. The EFS-4 is however, a bit large for the engine and can result in poor fuel distribution and lean operation at wide open throttle.  Although this can be made to work by limiting the throttle travel to less than wide open, it is not recommended. For maximum performance use the EFS-3A.