On the bench the reed looks to be sealing the seat perfectly. Unless the reed is distorting and bending out of shape during operation I'm not sure it's a sealing problem. Although it would be of interest to try the waist cut it would be of academic interest only as you've shown that there is no improvement. Besides I've only got one more stock reed to experiment on and I'd rather not bugger it up!

I think it's more likely an inertia problem. The reed has got to change direction 7000 times a minute. That's over a hundred times a second! I bet with so little spring force on the reed it's lagging behind in getting back down to the seat as the crankcase pressure builds up on the piston's down stroke. In fact it may be still on the way up as the crankcase pressure turns around from negative to positive!

Measuring the force to open the reed on your set up with the waist cut in the reed might be interesting. If you have a digital postal scale or a spring postal scale or kitchen scale you can get a good idea what the force is. I took a tooth pick, stuck it into the intake port at the edge closest to the opening end of the reed and balanced the whole backplate assembly over the platform of the scale (the end of the toothpick rests on the scale platform) and pushed down until the reed was just barely off the reed stop set at 1/8th inch. If the scale measures in ounces there are about 28 grams in an ounce so you can compare what I got.

As for the newer style cylinder with four transfer runners, I believe there are huge gains to be made by smoothing out the entrance to the transfer ports. The flow coefficient, and thus the effective flow area, of those ports just has to be abysmal with those blunt facing surfaces facing the flow. I not only bullet-nosed the web separating the two runners but also matched the outer edges of the ports to the crankcase so nowhere are there forward facing steps in the flow path. I bet you are right about the difference in cylinder volume (compared to the older cylinder, ie compression) but I'm not sure how to improve that situation with my setup. The only other cylinder I've got is the one with decompression slots.

diceco