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CB750/500 petrol tap renovation

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Oddjob:
Got to disagree Graham, it’s both, stops air getting in and thus stops petrol vapour getting out. There must be some exposure to the petrol or even if the oring fails it wouldn’t be able to access the air inlet tract. The main difference is that the vacuum in the inlet tract mainly encourages ingress of air rather than the other way round but something like a backfire through the carb would allow exposure the other way as well.

It can’t hurt to eliminate the chance of ethanol exposure to the oring by replacement with viton rather than nitrile. Same to some extent could be said about internal engine orings, we’ve all smelt petrol in engine oil for example, is that harming the nitrile rings in the engine?

Not arguing this is the case just seeing what the general thoughts on this theory are.

Nurse Julie:
We use Viton O rings on all engine oil ways and of course the oil pump. The only Nitrile we use are on the tappet caps as its not an oilway and Viton is too hard for there anyway. Having had 2 jars of Ethanol petrol on the bench for 3 years now, one with Viton and the other with Nitrile submerged, yes, the Nitrile has disintegrated totally, ie, gone all stretched and sort of melted, the Viton hasn't been affected. But, the O rings suspended in the jars on lengths of wire, suspended above the fuel, therefore only in the fumes, neither have disintegrated........so far 😊😊😊😊

Oddjob:
Interesting Julie. So if that is correct and I have no reason to doubt it, then only by being submerged or constantly exposed to fuel causes the Nitrile rings to deteriorate, exposure to vapours and such either doesn't or takes far far longer to become apparent.

I wonder as the levels of Ethanol increase whether the deterioration increases as well. A couple of years ago it was 5% now IIRC it's already at 10%. Saying that they have E85 fuel in the US and certain European countries, that's 85% Ethanol and only 15% petrol. You can almost see the orings melting can't you?  ;D ;D

taysidedragon:
I'm sure that when Ethanol was introduced into the petrol the recommendation was to replace o-rings and rubber seals in the fuel system as a whole. That would include the fuel tap.

Oddjob:
Got to say that nowhere to my knowledge has anyone said anything about replacing any orings except for this forum. When I mention it to other bikers for instance they are totally unaware of it, as I’m sure are 99% of car drivers.

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