How do I seal my fuel tap / cutting out when warm nc21z

[Dpazza]

Thanks for the replies.

I did not say it is an NC21z.
To update I have changed the tank as the original tank did have too many small holes! The new tank has been properly welded and pressure tested. The problem is that the actual fittings on the base of the tank are different, the original tank had a raised lip which went inside the tap unit to seal, the new one has just a flat surface with space for an oring seal (so guessing this may be a later tank?)
I have managed to salvage an original seal from a bag of bits to fit the petrol tap unit (very thin right angled rubber o-ring) and put back together with some red hylomar and it seems to have sealed so far.

Longer term i would like to fit the o-ring seal, is this a standard part NC24/30? and who might stock it.

Thanks
Dave

[Dpazza]

Apologies my second post in quick succession, I have changed the petrol tank and taken it out on it's first decent run today.

The problem is, when the bike gets warm (just under half on the temp gauge the bike cuts out and refuses to start again until after 10-20 mins it has cooled sufficiently?
Although the gauge reads just under half, the crankcase feels very hot, I have not been able to see if the cooling fan is cutting in.

Can anyone suggest some items to check? Is it a problem with the fuel supply? - the tank is half full and tried different settings (on/res)

Thanks

[arsey30]

Check tank breather hose for blockage [ squashed] and vacuum hose for leaks.

[Neosophist]

Thanks for the replies.

I did not say it is an NC21z.
To update I have changed the tank as the original tank did have too many small holes! The new tank has been properly welded and pressure tested. The problem is that the actual fittings on the base of the tank are different, the original tank had a raised lip which went inside the tap unit to seal, the new one has just a flat surface with space for an oring seal (so guessing this may be a later tank?)
I have managed to salvage an original seal from a bag of bits to fit the petrol tap unit (very thin right angled rubber o-ring) and put back together with some red hylomar and it seems to have sealed so far.

Longer term i would like to fit the o-ring seal, is this a standard part NC24/30? and who might stock it.

Thanks
Dave

Do not use gasket goo on a fuel tap, it will mask any bad fitting leaks and will fail at some point, leaving you with a fuel all over the place

It sounds like your previous tap was a bit of a bodge job?

All NC21/NC24 should use the same tap.

ＶＦＲ４００Ｒ / ＶＦＲ４００ＲＧ （ １９８６年モデル 型式ＮＣ２１ 適合フレームナンバー ＮＣ２１－１００００１１～１０１５７５６ ）
ＶＦＲ４００Ｒ / ＶＦＲ４００ＲＨ （ １９８７年モデル 型式ＮＣ２４ 適合フレームナンバー ＮＣ２４－１００００１０～１０１７０５０ ）
ＶＦＲ４００Ｒ / ＶＦＲ４００ＲＪ （ １９８８年モデル 型式ＮＣ２４ 適合フレームナンバー ＮＣ２４－１０２００１１～１０３２６６７ ）
ＶＦＲ４００Ｚ / ＶＦＲ４００ＺＧ （ １９８６年モデル 型式ＮＣ２１ 適合フレームナンバー ＮＣ２１－１００００７７～１０１５５５６ ）
ＶＦＲ４００Ｚ / ＶＦＲ４００ＺＨ （ １９８７年モデル 型式ＮＣ２１ 適合フレームナンバー ＮＣ２１－１０２００１３～１０２１４０７ ）

※※ 適合フューエルコックＡＳＳＹ品番 １６９５０－ＭＬ０－００４ / １６９５０－ＭＬ０－０１４ ※ 対応

As mentioned above.

Check your vaccum hose (if you havent replaced it put a new one on, it WILL fail at some point and leave you stranded) It runs from the outside of the left hand cylinder by the frame to the outermost spigot on the fuel tap.

Tank breather is also good call... if it cuts out immediatly open the tank and see if you can hear a whoosh of air, this will indicate the breather is blocked and you have vaccum in the tank.

Also you might have a bad tap, diaphram could be collapsing at higher temp and cutting off the fuel.

Start with the easy 2 suggested by arsey30.

Also the O-ring is available from any Honda dealer, part number 16958-mf2-880 local Honda dealer or Davild Silver Spares / Rick Oliver on this forum will be able to supply it.

There about 2.30 if I recall.

[Dpazza]

Brill, thanks for that I will check before heading home tonight, thanks

[Dpazza]

Quick update, seems to be a collapsing vaccum tube. So part on order along with the o-ring seal for the fuel tank. Thanks Chaps.

[Neosophist]

Very common.

Change em every 6 - 8 years and you should never have a problem wtih them. I always stick a sticker on them with the date it was installed..

[Dpazza]

Another update, thought I had solved the cutting out. I have changed the vacuum hose which had perished and assumed this was the problem. Have checked the breather hose and when it does cut out have opened the tank. Have not found pressure release whoosh which indicates blockage.

The problem seems to be when the bike gets warm and up to temperature, on a constant throttle or not stop start the power suddenly cuts (as if cut off switch is operated?) - have checked I have not caught etc. When you coast to a halt it will refuse to start - the starter operates but it appears that no fuel is getting through. When you leave it for 15-20 mins it will start again and then run for a variable length of time before re-occurring.

The diaphragm was mentioned, is this something which is available and I presume it is the part when you take the tap apart which is easily accessible? Is there anything else I am missing as it means I do not trust my bike on journeys.

Thanks
Dave

[Neosophist]

test the electriacl output first.

then investigate the diaphram.

[Dpazza]

Forgive me for asking obvious questions, but when you suggest electrical output I presume you mean spark? Is there a way to test this at the side of the road? Or might this indicate a coil problem? In which case can it be tested before the problem occurs or does it have to be when it is warm?
Thanks
Dave