IIRC some of the reed manifolds for these engines actually increase the intake restriction, the purpose of windowed piston/ reed boxes in 1970's DS motorcycles was to broaden the torque and flatten to power band a little for trail riding.
In especially small displacement piston ported bikes like the Hodaka Ace 100, going to a reedbox and windowed piston in the later Road Toad 100 lowered the RPM point at which the engine's powerband 'came on' while not killing the topend. It's a delicate balance and these engines are a pretty old school piston ported design. You really would need to come up with a better cylinder casting with a reedbox and 3rd port widow below it for it to be a better engine.
Good point on reed restriction and power band observations Citi. All reeds and all reed setups are not equal, nor are they designed to provide equal benefits thru the entire power band & I've found that various expansion pipes used in conjunction with a properly designed reed induction system is also one of the keys to enjoying the benefits of the reed.
When RSE & other vendors started marketing focused on the China Girl owners; they greatly "oversold" their product and the benefits that one might expect from using their reed designs. Cutting piston windows was never mentioned, nor was machining a third port in the jug ever noted as modifications that were mandatory to taking advantage of the reeds operation. I modify both the piston and the jug. So a lot of folks got burned on reeds. It didn't take long and some, Norm at Venice was one, started working on solutions that would work and make power in properly modified motors. I use the RSE reed & a piston window along with 3rd. port jug. I machined both the piston and the jug to take advantage of the reed & two states of tune as I explained above: the kit muffler setup benefits more in the low to midrange, while the KTM expansion chamber really smooths out & comes on pipe at 7,500 rpms & will crank on out past 12,000 of course the real power lays between 7/5K and 10 K rpm's, not really gaining anything in the power sector at those higher rpm's.
So some of us have made those necessary engine changes and I for one enjoy the performance they provide. I have another traditionally modified piston port motor that really makes good power, but my reed port engines blow it away, apples for apples, both motors running KTM expansion pipes or both with stock kit muffler. In fact the traditionally tuned engine, with higher compression, ramps, ported etc. is really more cranky at low rpm's than the reed motors (I ride two with identical reed engine setups).
Two things I'll add as reed valve benefits: first blowback through the carb is minimized and secondly lubrication and cooling of both the wrist pin and the piston is vastly improved by that straight shot of fuel mix through the piston window to the piston interior.
Reed boxes I'm still working on, but haven't noticed any real improvement in performance to this point. I believe a power boost is there waiting to be found but I haven't seen it yet.
Substantial power improvements typically require work and alterations, even to the so called bolt on mods, but sometimes it's really worth the effort. I'm certainly pleased with the results I've received.
Rick C.
