If Rod is burning 40L/h in his Lyc 180, he obviously doesn't know how to lean properly.
Plus, comparing the fuel burn on a 180hp Lycoming to a 100hp Rotax is a little disingenuous. I think you'll find that a properly operated certified Lycoming will be close to competitive with a Rotax (on a BSFC basis), and in a PFA aircraft with an electronic ignition system, even more so.
Rod is obviously blinkered when he says the Lycoming is 1940's technology. If he were given the design brief to deliver 180hp at a Lyc power/weight, he would struggle to achieve much better without turning out something that looked pretty much like a Lycoming.
A
PS: even at the extortionate 25L/h premium over the Rotax that Rod claims, it's still relative peanuts cost-wise compared to the other costs of running an aircraft for a typical 100hrs/year flyer. 100hp might do 140kts, but how much can it lift and how fast?