Originally Posted by Cretin
95 octane listed, the lower compression twin spark 650gs runs ok on 91, 12.3:1 sounds too much for 91 octane
maybe, maybe not. so many other factors have a bearing on whether it will run happy on 91. Valve timing/overlap, ignition map, also fuel injection can run a higher air/fuel mix than carbs . there's a bucket load of parameters.
what probably will happen is the engine management will retard ignition to stop the knock and it will suffer from worse power and fuel consumption as it runs the engine in a less optimal part of the mapping.
My single sparker gets best performance & economy from 95
no easy answer.