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CB750/500 petrol tap renovation

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Oddjob:
Just ordered a new bowl and doughnut seal from DS. Also after a re-measure with a digital vernier I concluded that the bowl O-Ring is more 31mm than 30mm, the thickness was around 2.67mm and concluding that it must have been squashed in use I think the initial thickness was more like 3mm, so I ordered some Viton O-Rings at 25 x 3mm and just in case some 26 x 2.5mm, I'll see which suit better when they arrive. The tap to tank O-Ring looks to be 2mm but again it's almost flat, so to cover all the bases I ordered some 23mm x 2mm and some 23mm x 2.5mm and again I'll see which suit better.

I'll wait for the new doughnut to arrive to see what thickness of Viton sheet I should order to make some new ones.

Orcade-Ian:
Ah yes Ken,
The long brass tube goes right down to the body of the tap with no side hole and there's a separate hole for reserve.  Otherwise you would have no reserve!  Must go back to skool!

Ian

Seabeowner:
As I say I've been using 23 x 2mm c/s and 28 x 2.5 for about 4-5 years on a couple of bikes and I think they may be nitrile. Know that as the bowl one expanded a bit and had to stuff back in but actually seals just fine.

Oddjob:
It's odd, don't you think, that people and recommending we use Viton O-Rings because of the Ethanol in todays modern fuel. We are advised to replace all the O-Rings in the carbs due to the exposure to the new fuel YET no one says anything about the petrol tap O-Rings. Yet if anything the tap is exposed to more fuel than the carbs, we drain the float bowls in Winter be we don't drain the tank so the tap is constantly exposed to the Ethanol. We also say nothing about the inlet manifold O-Rings which are exposed as well, not as much as the carb and taps admittedly but they act as a seal against the outside environment so they must be exposed to some of the petrol vapour but we don't say anything about replacing them.

At 28 x 2.5mm I'd say the ring was 2mm oversize, which may explain why it needs to be stuffed back in. I'll see when the new rings arrived. I think the 23 x 2mm was pretty much spot on. I'll see though if 2.5mm would be better or worse.

Trigger:
Inlet manifold o'ring is a air seal and not a fuel seal and it does not come in contact with fuel  ;)

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