McFarlane Fuel Primer Improvements

By Dave McFarlane

During the development of our new Fuel Primer, we tested several used units and discovered that they were leaking fuel through to the engine. Over time, the small amount of leaked fuel builds up in the engine intake tubes or cylinders, and on some engines, fuel will drip out of 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. The new McFarlane Primer features Viton seals in the check valves to cleanly shut off fuel when it is not in operation. The McFarlane Piston Knob assembly features optimized seal grooves for smooth operation during use. McFarlane’s improved seals for the Piston Knob assembly replace the old, damaged, worn, and sticky O-rings that are often difficult to operate and function. The barrel material and coating prevent corrosion and wear that is found in many installed Primer assemblies. Our use of a Delrin wear washer ensures smooth plunger operation and prevents scraping, which was found on most original barrel and piston assemblies. 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. 

Each Fuel Primer assembly is tested before leaving our facility in Baldwin City, Kansas.