O-ring for sealing the Dellorto PHBH carburetor float bowl to the carburetor body: Dellorto part number 9424
Moto Guzzi 250 TS, 350 NTX, 650 NTX, 750 NTX, 750 SP, 750 T, 750 XPA, Breva 750, Nevada 350, Nevada 750, STR V750 IE, Targa 750, V35, V35 Florida, V35 II, V35 Imola, V50, V50 II, V50 III, V50 Monza, V65, V65 Florida, V65 SP, V7 Café Classic, V7 Classic, V7 II Racer, V7 II Special, V7 II Stone, V7 Racer, V7 Special, V7 Stone, and V75 models
The size of the O-ring used to seal the Dellorto PHBH carburetor float bowl to the carburetor body is 66.4 mm ID × 1.78 mm wide (UNI OR 2262). Viton O-rings are best, but Buna-N work just fine and are a lot cheaper. Make sure to purchase an O-ring that is sufficiently soft...something with a Shore Durometer (A Scale) = 70 is great.
Charlie Mullendore of Antietam Classic Cycle reports that McMaster-Carr part number 9464K381 will work well (Dash 038, Viton 75 durometer). Thanks to Charlie Mullendore for sending me this information in a private communication. In Charlie's own words:
They fit *exactly* like original Dellorto bowl O-rings - they need to be stretched slightly to stay in the groove.