This all has been a very interesting topic and read it front to back. It seems topical and resurges in interest often with different makes and models. Some years back I worked a spell on a bike backlog for a local shop and they carried a number of bikes modern and vintage. The owner was very interested in the BUNN Breather issue for some of the modern Enfields as we built hot rodded versions for some customers. People tend to get tunnel vision and not look beyond their specific make and model. At that time I amassed a huge amount of discussions and tech materials from a wide range of sources and shared it with the brain trust at that shop.
We concluded that the BUNN breather had merits but anyone could make their own versions and I suspect thats what did in the supplier.
The plumbing has been known for decades.
The trick was to find the right material for the valve that would not resonate anywhere in the frequency of the engine pulses.
Rex was a chemical engineer and eventually found a material that worked.
A sheet of it was a hock your house type price so he then hunted out users of the material , bought their scrap & hand cut all the valves from that in order to keep the price down.
Rex has a shortish attention span so after a while he was looking for a buyer but there simply was not the interest so he stopped making them and went into movie making producing 3 doccos and writing another book which includes everything he found out with the exception of the valve material.
Yes there are thousands of check valves out there.Rex and eventually the University of Auckland tested each & every valve available at the time but none worked over the entire rev range 1000 rpm to 10,000 rpm, temperature range & volume range
Some worked at low speeds & some worked at high speeds but none worked at all speeds except his.
What Rex failed to take into account was that while he wanted & was willing to pay for perfection the average British bike rider is way too cheap to pay $ 40 for his valve when they could go the el-cheapo car parts & buy a PCV valve for $ 3.95 plus 4 foot of PVC tube and that is exactly what happened .
Everything in the kit was unique to the kit
The valve , the thickness, density & size of the tubing were all specially made so they worked together.
All the current knowledge about engine exhaust went into the kits which is why they were supplied with very specific instructions about tube length for different bikes.
The kit of the B31/33 does not work on an A10 right out of the box and visa - versa.
Even the book he wrote with the results of 15 years of research never covered publishing costs.
