Dear All,
I have a Rotax 912 in a flexwing trike airframe. Since new the engine has run rough between 3500 - 4500rpm. Before going back to the aircraft manufacturer I checked carb balance, carb heaters, changed the prop to a different type, tried different needle positions and checked that all in genaral was OK - with no change to the vibration. It then went back to the aircraft manufacturer who rechecked everything, took cylinder compresion readings (130/135 on one side, 120/140 on the other). No improvement.
Above 4500rpm and nelow 3500rpm the engine is sweet. Between those values it has a high frequency vibration felt through the airframe and if you look at the engine the carbs are bouncing around.
On previous 912 engines I have always lowered the needles 1 notch lower than standard (3 from bottom) - which is how this engine is now tuned - but I have also tried both standard and 1 notch richer settings and these make no difference to the vibration.
Carb balancing gauges show no irregularities in the vibratory rev range.
Before returning it to Mr Rotax does anybody have any further ideas please?
Many thanks
Andy Buchan
I have a Rotax 912 in a flexwing trike airframe. Since new the engine has run rough between 3500 - 4500rpm. Before going back to the aircraft manufacturer I checked carb balance, carb heaters, changed the prop to a different type, tried different needle positions and checked that all in genaral was OK - with no change to the vibration. It then went back to the aircraft manufacturer who rechecked everything, took cylinder compresion readings (130/135 on one side, 120/140 on the other). No improvement.
Above 4500rpm and nelow 3500rpm the engine is sweet. Between those values it has a high frequency vibration felt through the airframe and if you look at the engine the carbs are bouncing around.
On previous 912 engines I have always lowered the needles 1 notch lower than standard (3 from bottom) - which is how this engine is now tuned - but I have also tried both standard and 1 notch richer settings and these make no difference to the vibration.
Carb balancing gauges show no irregularities in the vibratory rev range.
Before returning it to Mr Rotax does anybody have any further ideas please?
Many thanks
Andy Buchan
