Pirep: McFarlane SB-6 / Replacement Carb Spring (6818)

McFarlane SB-6, July 10,2014
Part Numbers Affected: 6748 Spring
New (replacement) Part Number: 6818 Spring

Background: Re-design of spring requiring part to receive local annealing of work hardened areas. New part number identified by presence of blue or green stripe applied to side of spring. Failures reported were at extended end of spring.

Pirep: Received 2-sets of new springs (p/n 6818); Installed one set on N901EN and the other set on N906EN. Both sets (all 4 springs) failed in less than 10 hours of operation. **All failures at short loop.



Edit: Throttle operation without spring loading was a non-issue on both aircraft. Except for the absence of pressures required to operate the throttle (kind of nice), all operations were normal.

Though the engine will operate safely, my experience is it is not fully normal.
Without both springs in place, the carbs are not fully in sync and a noticeable amount of roughness is evident at throttle settings at or near idle.

This is a classic example of why Van's issued a notice to not use paint stripped springs. 10 - 15 hours until failure seems to be typical.

Hey Ernie... what is that on your nose?