143bhp

[Falcon 269]

You'll probably find that you can't get the O-rings separately from a Yamaha dealer, as they're included as part of a carb rebuild kit that also has the float valve needle and other bits in it.  I guess a friendly dealer might let you have suitable O-rings from his workbench stock, though.

I just ordered some online from an ebay listing:

https://www.ebay.co.uk/itm/7-5-x-1-5mm-V...2749.l2649