Narrative:

I flew most of the flight VFR at 11;500 ft; OAT gauge indicated 46 F. Later in the flight I needed to air file and received an IFR clearance due to low ceilings at destination. While descending into very hot and humid conditions; I was instructed to descend from 6;000 MSL to 5;000 MSL. Passing approximately 5;200 MSL I noticed a considerable loss in engine power. I also noticed the #2 egt had gone to zero on gem 602 engine monitor. Other egt's were lower than normal but still indicated something on the engine monitor. [I] could not maintain the assigned 5;000 ft without a significant reduction in airspeed. I attempted to apply carb heat but this seemed to reduce engine RPM even further. I also increase the mixture to a more rich setting but this also reduced engine RPM. Found best power with carb heat off and a very lean mixture. I then notified approach that I could not maintain altitude and needed to proceed direct to destination. Further noticed that I was passing over an en route airport and advised approach that I would like to land there. Approach cleared me to proceed as requested and advised me of the runway direction; length and width. I asked if I should switch to the airport's unicom frequency or stay with them; they advised that they showed no traffic in the area and to stay with them; and to radio them when safely on the ground. I set up for an engine out approach; but the engine continued to give partial power throughout the landing. I landed and taxied to parking without incident. While parked I preformed a mag check and adjusted the throttle and mixture to restore full static power. After adjusting these controls a few minutes I managed to restore full static engine power. I suspect the root problem was carb icing which melted out within a few minutes of landing. Further suspect the carb heat might have eventually melted the ice while in the air; had I given it more time. I called approach from the FBO.

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Original NASA ASRS Text

Title: Long EZ pilot experiences loss of engine power during descent in humid conditions. Carb heat does not solve the problem and the reporter elects to divert to a suitable airport. The engine continues to run and full power is restored once on the ground. Carb ice is strongly suspected.

Narrative: I flew most of the flight VFR at 11;500 FT; OAT gauge indicated 46 F. Later in the flight I needed to air file and received an IFR clearance due to low ceilings at destination. While descending into very hot and humid conditions; I was instructed to descend from 6;000 MSL to 5;000 MSL. Passing approximately 5;200 MSL I noticed a considerable loss in engine power. I also noticed the #2 EGT had gone to zero on GEM 602 engine monitor. Other EGT's were lower than normal but still indicated something on the engine monitor. [I] could not maintain the assigned 5;000 FT without a significant reduction in airspeed. I attempted to apply carb heat but this seemed to reduce engine RPM even further. I also increase the mixture to a more rich setting but this also reduced engine RPM. Found best power with carb heat off and a very lean mixture. I then notified Approach that I could not maintain altitude and needed to proceed direct to destination. Further noticed that I was passing over an en route airport and advised Approach that I would like to land there. Approach cleared me to proceed as requested and advised me of the runway direction; length and width. I asked if I should switch to the airport's UNICOM frequency or stay with them; they advised that they showed no traffic in the area and to stay with them; and to radio them when safely on the ground. I set up for an engine out approach; but the engine continued to give partial power throughout the landing. I landed and taxied to parking without incident. While parked I preformed a mag check and adjusted the throttle and mixture to restore full static power. After adjusting these controls a few minutes I managed to restore full static engine power. I suspect the root problem was carb icing which melted out within a few minutes of landing. Further suspect the carb heat might have eventually melted the ice while in the air; had I given it more time. I called Approach from the FBO.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.