Carb Sync Education
Hi All,
First condition inspection one year of ownership and 60 flight hours after carb rebuild, new sprag clutch, rubber replacement, and gearbox inspection by a Rotax-certified A+P on a 1998 912ULS in a Rans S7 with 700 hours. I'm trying to educate myself and my A+P/IA on carb sync. Before I set the mixture screws to 1.5 turns out, I found the current positions at 3/4 turn on one carb and one turn on the other. After enriching to 1.5 turns, syncing carbs, and replacing plugs, it starts on first try where it had begun occasionally taking two tries. It also recently has a high pitched, but not very loud whine at idle that comes and goes abruptly with no change in input or output/gauges. The only significant change during inspection was compression on #4 cylinder went from 78 to 62/80 (still at 62 after a two hour flight).
--the manual still recommends setting mixtures at peak RPM vs video says 1.5 turns out. Since a dual manifold pressure gauge is used to sync throttle cable positions, any reason not to use that to set mixture at peak power, or should I stop overthinking it and just use 1.5 turns?
--possible that previous A+P found peak RPM at that lean setting?
--risk of damage from lean setting that would affect compression or engine noise?
--when it wasn't starting on first try, the prop came to an abrupt stop but not a reverse motion. It caused a significant shudder of the 700# airframe, about the same as shutdown one ignition after the other. Is some vibration normal or is there risk of damage at start or shutdown even if prop is not "kicking back"? (Soft start modules are on order).
Thank you!
