Tactical fuel tap replacement

[Swingarm]

Hey folks

My NC30 turns 25 years old under my ownership this year.

In that time the fuel tap has worked flawlessly and never been replaced.

My question is, in regards to the known deterioration/issue with the diaphragm, is it worth pre-emptively replacing it or assume it will continue to be ok, until it fails?

Thanks

S

[CMSMJ1]

If the diapragm fails it would only mean the tap is "always on" without a vacuum. As long as you'd physically set the tap to off you **should** not notice any difference at all.

Saying that, it's not a bad call - as you mgiht not set it to off and it might dump the tank into the carbs and if your carbs allow the fuel through you'll end up with a lot of fuel in your oil. That's a pain in the arse.

[Neosophist]

I just checked with Honda you can still get a new fuel tap (around 100 uk pounds) but no idea when they last manufactured them so you might end up with 10 year old rubber anyway.

A few years ago you used to be able to get rebuild diaphragm kits (no idea on quality) might be worth picking one up for spares and keeping it in stock if they are cheap or even just change it out for peace of mind.

It's an easy bypass / replace if it does fail.. if the diaphragm fails though doesn't it shut the fuel off as it cant suck the diaphragm open / also possibly flood engine as fuel leaks past down into the vacuum hose.. been a while since I've looked at an NC30 fuel tap.

It's a secondary safety thing.. if you leave the fuel on and if the floats start leaking you won't fill the engine with fuel / leak it all on the ground.

Most of my pre 70s bikes don't have any kind of vacuum tap and some of them get left with the fuel on for months at a time and dont leak as the float needles are in good condition.. always best to turn them off though as fuel will evaporate from the floatbowls and if the fuel is on they will keep filling back up.

ethanol seems to be the biggest issue with old rubber.. fortuantly no ethanol fuel here, ive always had the most trouble with the rubber hose to the vacuum taps failng, if you havent replaced this line then id replace that at least, 4mm honda vacuum hose you can get a 5 meter coil of it for pennies.

[Swingarm]

Thank you, Neo. That's helpful

[CMSMJ1]

I just checked with Honda you can still get a new fuel tap (around 100 uk pounds) but no idea when they last manufactured them so you might end up with 10 year old rubber anyway.

A few years ago you used to be able to get rebuild diaphragm kits (no idea on quality) might be worth picking one up for spares and keeping it in stock if they are cheap or even just change it out for peace of mind.

It's an easy bypass / replace if it does fail.. if the diaphragm fails though doesn't it shut the fuel off as it cant suck the diaphragm open / also possibly flood engine as fuel leaks past down into the vacuum hose.. been a while since I've looked at an NC30 fuel tap.

It's a secondary safety thing.. if you leave the fuel on and if the floats start leaking you won't fill the engine with fuel / leak it all on the ground.

Most of my pre 70s bikes don't have any kind of vacuum tap and some of them get left with the fuel on for months at a time and dont leak as the float needles are in good condition.. always best to turn them off though as fuel will evaporate from the floatbowls and if the fuel is on they will keep filling back up.

ethanol seems to be the biggest issue with old rubber.. fortuantly no ethanol fuel here, ive always had the most trouble with the rubber hose to the vacuum taps failng, if you havent replaced this line then id replace that at least, 4mm honda vacuum hose you can get a 5 meter coil of it for pennies.

Nice to see you mate

[Neosophist]

yeah man you too! still got your nc30? I sold my last one about 8 years ago now.. been trying to cut down the number of bikes I have, down to 9 now. but the only ones that ever get ridden are the 954 for highway use and my little suzuki 110 2 stroke scooter for everything else..

[CMSMJ1]

We'll cope with the thread drift eh?

Aye - have got no9 still. Not been MOT'd since 2014 as was used for track duties. Spannered myself on a ZX10 at Jerez in 2018 (how time flies...) and that put me right off. Spent 2k getting no9 recommissioned and then tried to get my mojo back. Crashed it (a nice crash - almost enjoyed the normalcy of it) at Cadwell a couple years ago... not ridden since. Getting it road legal and will potter about on it.

Have a Bros too for the comedy commuter and just got a good deal on a 990 Superduke

Life gets in the way mainly...was a young man once...now I know how it feels to scrape middle age with the ballaches of responsbility I have no time.

Hope all is well, take it easy!

I stills ee people from here now and again, saw Paul the other week in fact and probably catch up a couple or three times a year.

[GrahamReeves]

So on my nc35 tap, I turn the tap to off to run the carbs dry but the tap still provides enough fuel to keep the bike running and not run dry... if I unplug the vacuum pipe it runs dry in a few minutes. I took the tank off and tested the tap by turning it to off and no fuel... applied a vacuum to it and it dribbles enough fuel to run... not as much flow as when on. It's not modded. The switchable part of the tap doesn't seem to be serviceable either. Is the tap working as it should or should it not flow any fuel at all when turned off and with a vacuum? Thanks

[Neosophist]

So on my nc35 tap, I turn the tap to off to run the carbs dry but the tap still provides enough fuel to keep the bike running and not run dry... if I unplug the vacuum pipe it runs dry in a few minutes. I took the tank off and tested the tap by turning it to off and no fuel... applied a vacuum to it and it dribbles enough fuel to run... not as much flow as when on. It's not modded. The switchable part of the tap doesn't seem to be serviceable either. Is the tap working as it should or should it not flow any fuel at all when turned off and with a vacuum? Thanks

Not normal behaviour no.

The tap is leaking when switched to off, the secondary safety (vacuum shutoff) is still working.

[GrahamReeves]

Hi... yes.. the vacuum protect works as the tap, when switched off, doesn't pass fuel but if bike is running and creating a vacuum it passes fuel. Granted not as much if the tap was switched to on but enough to keep the bike running and not drain the bowls. So knackered tap then I presume? Where's the ones at £110 as the ones I find are all over £200. Thanks