My 1990 VFR750 petcock was leaking. In my case, leaking from both the petcock body as well as through the outlet when the petcock was turned off. After reading a bunch on the forums I learned that it can be rebuilt. Some threads that were helpful:
https://www.vfrdiscussion.com/index.php?/forums/topic/87331-petcock-body-leaks/
https://www.vfrdiscussion.com/index.php?/forums/topic/82877-3rd-gen-fuel-petcock-o-ring/
Should have got the kit from NRP but I decided to homebrew it.
I thought I could add to the discussion here by providing details.
I recommend the following Viton o-rings.
Petcock to fuel tank: 24mm ID x 2mm wide, quantity one (not sure if still available as OEM? Disappeared from Honda p/n’s on revzilla, partzilla etc. but I found the size on one of the forums)
Side plate to petcock body: 29mm ID x 1.5mm wide, quantity one
Internal seal: 7mm ID x 1.5mm wide, quantity one (two if you are fastidious) (FYI I used 7mm ID x 2mm W and it was a little big, I’d recommend go down to 1.5mm W)
Shaft seal: 7mm ID x 2mm wide, quantity two
*If turning your petcock “off” doesn’t stop the fuel flow to the outlet after you rebuild, you’ll also need a new spring about 0.9 wire thickness x 9.5mm OD x 10mm L. You might have to try different springs depending on how firm or soft the new spring is, but this is what worked for me. I got it from this kit:
https://www.amazon.com/Compression-Assortment-Stainless-Different-Individual/dp/B0BL7RYQ27/ref=sr_1_4?qid=1707004725&th=1
So that’s the short version! If you want pics and step by step keep reading!