McFarlane Fuel Primer Improvements

By Dave McFarlane

During the development of our new fuel primer, we discovered that all the used units we tested were leaking fuel through to the engine. Over time, the small amount of fuel leaked builds up in the engine intake tubes or cylinders, and on some engines, fuel will drip out the carburetor. Although this leakage often goes unnoticed, it can result in rich engine operation at idle and low power settings, while wasting fuel or leading to inconsistent carburetor adjustment results. 

The original fuel primers relied on a metal-to-metal ball seal at the check valves and cut-off needle. However, the new McFarlane primer features Viton seals in the check valves to cleanly shut off fuel when it is not in operation. McFarlane’s improved seals replace the old and sticky O-rings that are often difficult to work. In addition, a brass barrel is used instead of aluminum for continuous corrosion protection and smooth feel. A nylon wear washer prevents scraping to ensure smooth plunger operation. The all-metal fuel plunger is now a one-piece unit that eliminates the original plastic knob. Lastly, enlarged primer ports provide better fuel flow in emergencies.

The primer is a safety device!

The fuel primer also serves as a safety device during emergencies. In the event of carburetor ice development, the primer can be used to pump sufficient fuel into the engine, enabling it to run long enough to make it back to an airport. Therefore, it is crucial to ensure that your fuel primer is functioning optimally to be prepared for such situations.

How is the primer sold?

The McFarlane primer is available as a complete assembly, plunger only, body only, and repair parts. In many cases, where the old primer bore is still good, the McFarlane plunger can be used for a FAA-PMA approved quick fix for your existing primer.