Re; “But I still think I'm correct about them, including the 700s, all having reed valves, at least when they left the factory. Every reference I've seen, including the Carole Nash one above, agrees on that.”
Then I suggest you do some more in depth research as, I am beginning to get a bit bored with you as once again I will have to correct you –the original TZ700 NEVER HAD REED BLOCKS !!!!!!¬!!!!!!!!!!
As they were an upgrade from the TZ500 to enter in the 750 class and used slightly detuned (again NON REED BLOCK) TZ350 barrels- and this is where the confusion lies also - as Yamaha called them 750s which they were not until the reed block 750s arrived.
I have had and sold a Spondon TZ350 with one NON REED – PISTON PORTED 700 barrel fitted!!!!
Re; "you can now buy aftermarket cylinders and crankshafts to take them out to over 500 cc. "
They are called Banshee 325cc cylinders not quite 500 unless someone some where has found a way to openup the crankcases to fit larger barrels!
OK, you are letting this get too personal. I'm not attacking you, just trying to get the facts correct. You have so far posted no references to support your claim that the TZ700 never had reed blocks. I have listed several that claim they did. I am posting additional references below, as well as some pictures of TZ700s clearly showing the reed valve cylinders. Believe them or don't, whatever you choose.
Yamaha's TZ750:
Where Legends Began ...
Kel Carruthers recalls the early days of the TZ700
by evan williams
“Although it initially displaced 700cc, the machine was called the TZ750 because it had been designed for the Formula 750 class in Europe.”
“The spec sheet tells the tale: the TZ700/750 was an in-line four two-stroke, with
reed valve induction and a fragile dry clutch.”
Carole Nash
Content Writer
Published: 11th August 2008
“It is a common mistake that the 750 four is just two 350 engines coupled together, nothing could be further than the truth as it is actually based on the 1973 factory 500 four GP machine and shares no common components at all with the smaller roadster based twin.”
“So later in 1972 Yamaha built their first F750 prototype, which was actually a 700cc, four cylinder machine.”
“Barrels were
similar to the
reed valve induction, TZ350 racer, featuring identical bore and stroke measurements,”
The mighty TZ 750
at
http://www.tz350.net/bigbrothers.htm#tz750
“Yamaha unleashed it's first production 4 cylinder 750 two stroke racer monster on the public in March 1974, in the shape of the awesome TZ750A. Priced at around $Aus3,500 this bike had in fact been under development as early as 1971. This ground-breaking model weighed in at 157kg dry and produced 90bhp @ 10,500rpm from it's watercooled 694cc engine. Formidable figures in the early seventies by any standard. Interestingly, Yamaha claimed the bike had the potential to produce almost 140bhp with TZ350 cylinders fitted.
Technically, though very similar to the TZ350 motor-wise, it differed in a few crucial areas, these being:
1. The head's squish band was reduced from the 350's 2.0mm to 1mm and it's combustion chamber was made a little deeper so as to keep the compression ratio to 7.3:1.
2. The exhaust port was lowered 1.5mm and four petal
reed valves added to help control the influx of fuel mixture from the 34mm Mikuni carbs and to help "tame" the power delivery of this awesome machine , along with an additional fifth transfer port, "inlet" port if you like.
3. The 64mm dia. pistons had inlet holes cast into their rear, though a few of the early examples did not have this.
4. The four cylinder firing order was 1 and 4 (simultaneously) then 2 and 3.
The picture below clearly shows the TZ700 with the same reed valve cylinders as the late TZ750 above it.
This is a closer detail picture of the reed valve cylinders in Wolfgang Fuchs original TZ700.
If you hunt enough on-line, you can find a lot more pictures of TZ700 engines, all showing reed valve intakes.
Ken