Proper fuel mix is 50:1.Don't skimp on the amount.

87 octane should work fine High test is a waste.Some older motors list regular gas at 89 octane.If yours refuses to operate well on 87 try 90 or what ever is the next higher in your area.If it insists on high test there is something amiss maybe carbon buildup.In that case try a decarb treatment.

Be sure to adjust your high and low speed mixture valves to the best operation.Make the final highspeed adjustment just a shade toward rich.