the 85 twin runs better on a 26x8 3W prop,the tips with this prop would break the sound barrier and would absolutely rip the 27 pound laser it was in,My 75 twin spark isn't broken in yet (only one tank of fuel through it) but seems to have more power than the 85 twin. From flying both engines I think I will like the 75 twin spark better in the long run after it is broken in.
The 75 twin spark is pushing 8 horse at less weight !!!! than my 70i at 6.5 horse.With an extra couple of cc's and one more plug this lighter engine is putting out and extra 1 1/2 horse compared to the 70i It's worth the weight savings over the 85 twin.
All my engines have the Tillotson carbs installed, and all have run super for me. I believe the only advantage the 85 twin has over the 75 twin spark is the smoothness of the twin versus the single.