Bear in mind that Ryobi has made 3 different 26cc weedie engines. GEN I, identified by a single crankcase casting and a metal backcover, had some problem with the breather vent such that it did not operate very well inverted. Ryobi redesigned it slightly to fix the problem and designated it the GEN II, which sports a black plastic back cover. This is the most popular version powering Ryobi's 800 and 900 series weedwackers.

Later on, Ryobi came out with a completely new 4stroke design for their higher-end "professional grade" garden tools. The GEN III engine has a 2-piece aluminum (or maybe magnesium) clamshell crankcase, which forms the wet sump, thus eliminating the need for a "drain pan" back cover. This version is supposedly much lighter and more powerful. The 1/4 scale Cub shown in the Jag Engines website ( now curiously missing) is powered by the this GEN III engine.

The 875r and 1079r that I actually use to wack weeds have the GEN II and GEN III engines, respectively. I like the Ryobi 4strokes for their functional simplicity. Lattely, others have come up with fancier 4stroke designs, some of which even uses gas-oil mix like the 2-strokes. To me, that defeats one of the main purpose of going 4stroke - eliminating particulate emission from burning oil.

Anyhow, I'll probably end up converting the 1079r just for the fun of it. For now, I've already got too many conversion engines than I know to do with.