johnybravo...yes, I'll grant you that even the best of the manufacturers (like Jett) are a bit vague as to what they mean by "rich". The Rossi instructions take a lot of working out in their fractured "Inklich" [img]i/expressions/face-icon-small-smile.gif[/img] because they suggest the exhaust should be greasy [img]i/expressions/face-icon-small-smile.gif[/img]

The Jett instructions to open the needle 2 turns more than factory set and that you may need to leave the plug connected for the first minute leads me to think it's maybe a full 4 stroke.

But like you said, the problem comes with quantifying what's rich. Because there are only 2 distinct sounds an engine makes then if you shoot for the point where it's either swapping between both sounds or maybe just barely into a clean 2 stroke then it's something that everyone can do. This at least lets plenty of fuel (meaning oil) go through the engine in its first critical moments. After the first one or two tanks even an ABC can be run in a full 4 stroke without any harm. This is done all the time in CL stunt.

When Super Tigre developed the ABC set-up it was to overcome a problem with their cast iron piston .15 speed engines (in those days all small speed engines were like that) in that if they went slightly lean the end result was a seized engine. ABC allowed them to keep running without damage for enough time to allow the pilot to shut the engine down. The lighter piston also allowed better balancing. But the idea was so good it eventually became almost universal. They also pioneered Schneurle porting but in a slightly different form to what we have now.