Not sure what you mean by the "new" 4-strokes. Possibly the 29cc Chinese built engines that seem to have replaced the B&S engines in Craftsmen weed whackers? Anyway if you do a search I am sure you can find threads on the following engines.
Honda GX-31 35
Ryobi 26
B&S 34cc 40cc
Subaru-Robin/ Fuji 34cc
Stihl 32cc 65cc
Shindaiwa 80cc

With the exception of the Shindaiwa, I have at least one of each. Anyone want to part with a Shindaiwa?

J