SOHC.co.uk Forums > CB350/400
400 four main jet o ring
ozzybud:
--- Quote from: Oddjob on December 01, 2025, 05:24:45 PM ---Is that the correct material Ozzybud?
Says NBR on the packaging and if memory serves that’s nitrile, which is not recommended for today’s fuels containing ethanol. Surely Viton or FKM would be a much better choice?
AFAICR the original orings were nitrile and so I’d avoid replacing with genuine parts for this application as the same problem will just reoccur. Unless Honda have changed the material at a later date to allow for this.
--- End quote ---
Yes Viton is safe for all modern fuels. Most modern automobiles use nitrile for their hoses and o-rings in the fuel systems.
Oddjob:
Actually not 100% true that, not safe for bio diesel for instance. Not a factor for us to concern ourselves with in this case. However, whilst nitrile is ok with fuel up to 10% ethanol as that figure increases so corresponding does its ability to cope with ethanol decrease. There are also warnings online about constant immersion in fuel with ethanol in it, which I would say around a jet upside down in a float bowl would qualify it as.
We are already at e10 in the UK and I would suspect this is the thin edge of the wedge and higher E numbers are already being planned.
My point being, why risk it, just fit Viton ones and have some peace of mind. The difference in price is negligible really, do it once and do it right is a good saying.
ozzybud:
Oddjob. Is it your job on this forum to disagree with just about every post that i make on here?
I post from my experience and what works for me. I ask you to do the same. Isn't this why you got booted from the forum?
Friends don't let friends put ethanol fuel into their classic cars .motorcycles and lawn equipment. It gathers water and ruins everything. In your daily driver its fine. But periodic use machines is a Hard No for me.
If you have to use E10 fuel I get it. We can get ethanol free gas in the states.
ozzybud:
This quote is from Hondaman on the us Forums. And i trust everything he says!
"If they were NOT Viton O-rings, they would probably work well. Since they are, though, the 3.5mm dimension might be tighter than the ID of the wasp-waist groove where it sits. With Viton you mustn't make it stretch more than about 5% of its ID or over time it will break: this is partly why Buna 70 remains king in the ethanol-laced fuel world, because it expands when ethanol hits it and shrinks again when it dries out. This prevents them from self-destructing."
exvalvesetdabbler:
It has been my experience also to see viton o rings not liking to be stretched. A lot of science equipment that I worked with used o rings to secure membranes onto sensors that required a bit of stretch to get them on. Nitrile was always ok. The black viton o rings would break or once stretched would not recover. On some kit large nitrile o rings were used as drive belts.
HNBR are ok if you can get them. TFEP | Aflas O-Rings are also used in the auto industry.
Regards
Dave
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