MacDizzy's Two Stroke Technology Exchange (MTSTE) - The two stroke engine capital of the internet.

Mossbarger Reed Cage

I had one of those cages years ago. It didn't work well - for me. Though it did work a little better when I heavily modified it (removed some port dividers) and fitted it with higher quality reeds of a different thickness (more).

On their page, I especially liked the bit flow (CFM's) - as if to say that's all that matters. In a perfect world (like the steady state flow within a four stroke engine), total flow matters more than it does in our unsteady state flow engines. We're dealing with exhaust systems that can literally suck mixture from the float bowl of a carburetor when the theory tells us it shouldn't happen (like when the piston is at or past BDC) - WTF? This would be the equivalent of the four stroke engine passing mixture with its inlet valves closed. It can't happen. I wonder why they don't mention the apparatus or the procedures used to test these parts.

We know that most of the flow from a reed cage happens via the amount of reed petal tip area it has - more petal area equals more flow. That cage has that feature to a very small extent - it's "V" angle is slightly flatter (less spread apart) than the standard valve at 52 degrees (I don't remember its included angle). To get it the valve has to be spaced away from the engine via the use of a thick reed spacer. There are a couple of better reed cages that provide that to a greater extent. One of them is the RAD valve with its dual reeds (or any cage fitted with dual stage reeds), another is the Delta Valve with its dual pairs of reeds. The Pyramid valve is an interesting piece. Though there is a reed petal on each end of the cage the design is such that they removed tip area from the normal reed surfaces to get what they wanted. I've never thought enough of that cage to take the time to measure the actual increase (if any - in fact I think it's area is probably reduced) because one glance at it shows me the design flaws. In addition to that blunder the end petals are held to the cage via two screws at its big end - remember these end petals are triangle shaped (read, super stiff petals). It is inherent in this design that these reeds become tensioned much more greatly since they are made from the same material thickness and material as the petals fitted to the standard part of the reed block. In fact all of it's reed petals are tensioned somewhat greater because they are attached with screws at the wide end on the petal and are hanging their thinner end in the mixture path. It has been my experience that this cage doesn't work - for me. Years ago I can remember modifying some stock reed cages by adding a reed petal on its ends. Since I was using a stock part the standard petal area wasn't decreased and I didn't use a triangulated petal there. Granted it didn't open much, but reeds don't have to, to pass mixture.

Flow benches are like dynamometers. They have a place but they are only tools to use to aid us in discovering what does and what doesn't seem to work. The operative word here is "SEEM." I say that because what works on the bench or dyno doesn't always translate into real world positive gains. Unfortunately these tools can also tell us what we want them to tell us. Specific jetting for the dynamometer always shows better power than could be had in a real riding situation because the pulls are so short they can be leaned out without fear of detonation. The flow bench can be made to show results favoring one product over another as well. The folks at GroupK explain this pretty well (please see - http://www.groupk.com/carbs99.html ).

In closing, anyone who doesn't believe the 38 or 39 mm carburetors don't work better to make more power with a modern 250 engine hasn't driven, or tested one. If this were not fact Honda and the others would ship their 250's with 34 mm or smaller carburetors, but they don't do that because even the 125's are using 36 's. That article (from the link you mentioned) is full of such bogus data it makes me sick to think that some folks will read it and accept it as the truth.

MacDizzy's Two Stroke Technology Exchange is the Two Stroke Engine Capital of the Internet.