They were meeting regs of the epa at the time they were developed t, but the epa tightened them drastically well after the strato engine was designed. Stihl and most other companies didn't think any two stroke would be able to meet the new regs, but RM kept refining their engines until they not only met, but surpassed the regs. It seems you might believe that Stihl developed the 4 mix in a very short period of time, but that isn't true. They were in the works from about the early 2000's or maybe even '98/99.
I had a link to a lengthy article by an industry reporter all this, but can't find it anymore. I think it is still in our old computer.
Originally Posted by Darryl G
I can also tell by looking back to see how they're hanging and often reach back and feel them to see how firm they are.