Incident Summary
A pilot experienced a loss of engine power during flight, which occurred low to the terrain. The pilot reported that the fuel burn rate had been increasing over a period of time and that the engine had previously failed to respond to throttle input. This was the second such occurrence.
Pilot Report
The pilot stated that his normal leaning procedure for best power operation at 5,800 feet mean sea level required more mixture control travel than usual. On the day of the accident, the engine again failed to respond to throttle input, leading to a subsequent loss of engine power at low altitude.
Post-Accident Examination
Examination of the carburetor after the incident revealed a black composite float that felt heavier than normal. One pontoon exhibited light damage to its smooth shell. The engine spark plugs were lightly fuel sooted, indicating a rich mixture.
Service Bulletin
According to Precision Airmotive Corporation's mandatory Service Bulletin MSA-1, which calls for replacement of composite floats with metal floats, field reports indicate that composite floats may be absorbing fluid and sinking. The bulletin states that a sinking float may result in disruption of fuel flow to the engine. Compliance with this bulletin is mandatory for some operators but optional for 14 CFR Part 91 operators.