Okay, so I might give everyone a good laugh for the day, I will ask this question.

Does a 1971 HT1 90cc have a reed valve? I have studied the diagrams, but don't see that this little motor has one. Any knowledge shared by the experts is greatly appreciated. 

Shoot us some pictures.
I am kinda interested too.
I was looking at that year HT1 in Partzilla and it has both Flange and Spigot mounts.
www.partzilla.com/catalog/yamaha/motorcy...1971/ht1b/carburetor

 

No reed valve. That started the next year with LT2. Interesting parts pic though & wonder if the bolt up type was for the Go Fast Cylinder as clamp type had limited room for oversizing. I assembled those bikes new out of the box & had a barn fresh--under a bush fresh lol-- one recently which i got running like new after freeing the piston from the bore. Green tank one. Had a demo one at work in "70 with the race kit & man it was 'so fast'--too fast for the primitive suspension. Can't recall if it had the bolt up carb on that but suspect it did.

Gave up googling for a race kit gyt cylinder but my HT1 showed up 'as i bought it home'. I'll leave the pic small so you 'don't have to hurt your eyes' looking at it. Be good to have a full size pic of yours sometime.

No Reed valve on the HT1 90.  Piston port only…

Gave up googling for a race kit gyt cylinder but my HT1 showed up 'as i bought it home'. I'll leave the pic small so you 'don't have to hurt your eyes' looking at it. Be good to have a full size pic of yours sometime.

Yep, Jeff is correct ! Piston Port.
I wondered why the Spigot mount tho...
had to download the Service Manual in the Tech Library above to see why, on page 16 it show the intake
 picture ( 4-3-1 )

It just made me like these little bikes even more now !
But the question remains about the Flange Mount picture on the Partzilla ( normally pictures in the broken line   de-notes MX version. ) which makes me think I need to check out the 71' HT1MX. 
hmmmmm

 

HT1B has a VM20SC  carb,
yamaha-enduros.com/index.php/workshop/wiki/22-1971-ht1b

HT1MX has a VM24SH
yamaha-enduros.com/index.php/workshop/wiki/23-1971-ht1mx

On a close inspection of the two brochures . The HT1 B has a spigot mount carb ,
and the HT1 MX uses a flange mount carb .
Never noticed that before either .

Hope we didn't scare Jimbo off !?!
Would like to see pictures of his bike ( Purple or Yellow ! )
William, your bike is a PEACH ! no need to hide it.
AND yes, Swoop.... it opened my eyes too. now I want one. MX version tho....

Sorry to hijack JIMBO !!