Pretty cloThe TZ 700 was actually at 698cc as it had two TZ350 piston ported barrels NO reed blocks were fitted. The TZ750 was a different bike altogether it was bored out to a pair of 375cc cyl blocks fitted, these barrels can be fitted to a piston ported TZ350 if the crankcase is opened up to fit.
Actorel, Yamaha never made a reed block TZ700/698CC this bike was an update (at the time) of a 500 racing bike like the one Kenny Roberts won the 500 world championship on - you might have seen one with a pair of LC350 barrels fitted that’s still a 700/698- you might have seen a twin shock TZ700 with a TZ750 engine in it-I don't know what you saw- they have been used on world record attempts with a 350 and 250 barrels on it just to claim a 600 cc record in the 1970s!!!
Pretty close
. Not meaning to dispute you, Bernhard. I'm used to the stuff you post as being very reliable. Maybe we are talking about two different bikes? So I'll just summarize what I think I know about the subject. Feel free to correct me.
I'm talking about the bike Yamaha developed as a factory Production 750 cc racer. The development was done in 1973, and I think the first customer bikes were produced in 1974, but I'm not completely sure about that timeline. It was developed by the same team, headed by Naito, responsible for the development of the YZR500, and was very similar to it, but with a bigger bore. The YZR500 was basically two doubled up 250 engines, with 54 x 54 mm bore and stroke. And it had Yamaha's new seven port "torque induction system", which had reed valves in the intake circuit. For the TZ700 they increased the bore to 64 mm, with the stroke kept at 54 mm, giving 695 cc. It was very similar to two TZ350350 engines doubled up, but in reality some of the major parts (crankshaft, piston, etc.) were not interchangeable with the TZ350 parts. But it still had the seven port, reed valve induction design. That was the bike Yamaha introduced as the TZ750A in 1974, and what I have been calling a TZ700. For the 1975 season they increased the displacement to 748 cc by increasing the bore to 66.4 mm. There might be some confusion here. The OW31 entries for Daytona F750 in 1976 were listed as 66 x 54 mm and 739 cc. I'm pretty sure someone just rounded the 66.4 mm bore spec down to 66 mm. All the TZ750 specs I've seen, except for the A version, list the bore as 66.4 mm.
There was at least one TZ700 prototype, and maybe more, built in 1972 or 1973, called the OW19, but it also had reed valves. After extensive testing with Kel Carruthers, they made some significant chassis design changes, and the resulting bike debuted as the TZ750A at Daytona in 1974.
There might have been other prototypes without reed valves, but I've never seen any reference to them.
My major sources for this info is "The Yamaha Legend" by Ted Mcauley, published in 1979, ISBN 0 85614 057 0, a couple of articles by Kevin Cameron, several other period magazine articles, the 1976/77 issue of Motocourse, a little bit of personal recollection, and, of course, whatever I could find on-line that I could trust. I found plenty of on-line stuff that was incorrect, too.
One of the best summaries of TZ750 history I found on-line is this one
https://classic-motorbikes.net/99/
And this one has a bit more info on the OW19 developing into the TZ750A.
http://www.95customs.com/the-1974-80-yamaha-tz750/2015/2/24
Ken