the expansion chamber draws the fuel charge into the cylinder via the transfer ports as the exhaust expands into the expansion chamber. then it reaches the reverse cone area and the back wave packs the charge back into the cylinder (with the reeds keeping it from going back out the carb). So pipe configuration and powervalve setting determine when and how much the cylinder gets "stuffed" Before expansion chambers and PV's 2 strokes were limited in power and range of power. some good info here... http://www.motorcycle.com/how-to/ho...ambers-work-and-why-you-should-care-3423.html
Now, if that air/fuel direct injection technology gets going, then you really shouldn't need an expansion chamber. All the fuel will be injected after the ports are closed. Any additional air that might have been swept in by the expansion chamber is taken care of by the air injection. Although that sounds a lot like supercharging. What was the name of that firm that's leading the way on this? Orbital. That's it. Oh, I just read an SAE article (well, most of it) about the Orbital air/fuel direct injection process, and it looks like the amount of air injected is very small, but at high pressure simply to atomize the injected fuel. Probably not enough added oxygen to counteract what an expansion chamber gives back. But I don't really know how much air is retrieved by an expansion chamber, either. Still really cool stuff, and I hope we get some direct injection two strokes soon.
You could always try to find a way to adjust the cone shape while riding, but so far I've only been able to reduce the volume of the expansion chamber while I'm on the trail, reversing the process has proven far more difficult than just bashing into a tree.
note , if you look at all the 2stroke trials bikes they really are sparce in the chamber dept, most look to have just a long standard head pipe on them with a tucked in frame shape driven chamber section. (my observation)
One thing with the trials bikes is they seem to have the motor tuned for one specific RPM band. When they are doing anything that needs power they seem to rev right to that power band and then go. Using the gearing to adjust speed.
Present USA Montesa importer has reserved www.ossausa.com. I hope we see them soon. I'm sticking money in my sock drawer!
