the running attitude in different grades all depends on the timing and compresiion of your engine higher the compression the higher grade fuel you should run,ignition timing can be adjusted a few degrees to allow for low grade fuel.my dad has an 89 150xr4 and it will hardly start on anything less than 89 it runs 125psi compresion my 200 johnson runs fine on 87 but it only has 105 psi it may turn 150 rpm more with 89 or higher.