912ULS Runs Rough at Idle
The 912ULS that is installed in my 2006 Evector SportStar (560TTSN) has suddenly started developing problems. The first problem happened while flying when the engine suddenly lost power for a half-second or two and then power returned to normal. The culprit was first thought to be the old cork gaskets in the carb bowls. They were replaced but the problem continued on the next Functional Check Flight. Then the carb floats were discovered to be decomposing and small flakes of float material were clogging both jets. Idle jets were blown and cleaned and both carbs were tuned and balanced, but a compression check was also performed and the #4 cylinder was only 66/86. Start and ground runup was normal. Climbed up to 7500 over the field, with all normal indications except the oil temps straying into the yellow side above the green band. When retarding the throttle to idle for the descent, noticeable vibrations were felt in the 3300-3800 rpm range. Above and below that, the engine seemed to run just fine. Upon landing, and the throttle retarded to idle, the rpms dropped to 500 and the engine almost conked out. When I added power to keep the engine alive, the engine ran very rough until the rpms increased above 2000. We are going to look at the #4 cylinder tomorrow morning, but just wondering what the collective brain trust might think. Been flying the airplane since 2015 and never had any problems, My background is retired USN and Southwest Airlines. Thanks in advance!
