Carb O-Ring Sizes: CB350, CB400, CB500, CB550

When rebuilding carbs on the old Honda fours with press-in main jets, you will often find that all the metal parts are fine after a good cleaning, and all that you really need to buy are new O-rings. Honda doesn’t sell the individual O-rings separately….

instead you have to buy a complete carb kit at $10 to $15 per carb. I found an industrial O-ring supplier who was willing to do small-volume counter sales, and was able to get new O-rings at about 50 cents per carb. Sizes are:

Main Jet: 1.2mm cross-section x 3.5 mm ID

Float Seat: 1.5 mm cross-section x 5 mm ID

Float Bowl Drain Screw: AS568-009 (7/32″ ID x 11/32″ OD)


Shifter lever seal = inside diameter – 14mm, outside diameter – 24mm, depth – 5mm

And the one behind the sprocket = I.D – 33mm, O.D. – 57mm, depth – 7mm