So the question came up on a FB thread and I don't think it was definitively answered.
I checked several sites for factory part numbers and of course now I'm just as confused as before.
Here's what I came up with...
1970:
No listings for YDS7 250 on any site
R5 350
Left- 278-14610-01-00
Right- 278-14610-01-00
Baffle -
278-14753-00-00
Or
278-14753-50-00
1971:
No listings for YDS7 250 on any site
R5 350
Left-
278-14610-01-00
Or
278-14610-61-00
Right-
278-14620-61-00
Or
278-14620-51-00
Baffle-
278-14753-00-00
Or
278-14753-50-00
1972:
YDS7 250
Left- 278-14610-01-00
Right- 278-14620-51-00
Baffle-
278-14753-00-00
Or
278-14753-50-00
R5 350
Left- 278-14610-01-00
Right-
278-14620-61-00
Or
278-14620-51-00
Baffle- 278-14753-00-00
Or
278-14753-50-00
So I couldn't find YDS7 part numbers FOR 1970,1971
For 1970 the R5 was offered with only one type pipe but 2 different Baffle?
In 1971 the R5 was available with 2 different types of pipes and 2 different baffles.
In 1972 the YDS7 Prts show up.
YDS7 shows 1 version of pipes and 2 versions of baffles
R5 shows 1 version of Left pipe, 2 versions or Right pipe and 2 versions of the baffles.
There's gotta be part books with 70 & 71 YDS7 listing somewhere.
Still trying to determine what the version differences are by part number.
Seamed, not seamed by year?
Baffle differences?
250 vs 350 differences?
pipes, the early r5 pipes have a seam. my 70 has those. the rest are the same pipes mechanically/visually.
r5 baffles are larger than ds7 ones internally, but either will fit either pipe, or rd 250/350 mufflers.
rd350 baffles fit right in, and actually flow better, i have some new reproduction rd baffles in my 70 r5.
i think the 2 part numbers is actually the superseded one, which is actually an rd 350 baffle.
(https://www.2strokeworld.net/wp-content/uploads/general-tech/baffles-side.jpg)
they did not sell the 70-71 ds7 in the states, only the 72. I know they were available in the uk.
my suggestion, use rd350 baffles.
https://yambits.co.uk/rd350-exhaust-baffle-p-47061.html
'seamed' pipes, early:
(https://www.2strokeworld.net/wp-content/uploads/70-R5/seat/r5seat-new_2.jpg)
non seamed pipes. these are actually r5 pipes, off a 72, but were identicle to the ds7 pipes except the baffle (on my ds7).
(https://www.2strokeworld.net/wp-content/uploads/72-ds7/seat/Resized_20220409_205858.jpeg)
Excellent breakdown mark thank you so much
As a random note, my 71 R5 had seamed pipes on it when I bought it. It spent 26 years in a basement so I'm pretty sure they were original to the bike.
Perhaps there was a cutover during 1971 seams->no seams.
the 71 i had also had seamed pipes, was an early one in production as well. so i agree that some 71s had them as well.