vfr 400 nc30 not getting gas

[el_scor_cho]

hey guys need a bit of help.
my vfr 400cc (1989 nc30) runs fine for a while then seems to starve itself of gas after 5-10mins. almost exactly the same feeling as when the reserve switch on the tank is needed to be switched on. have taken apart the tank pipes etc and all seems to be in working order. although the diaphragm at the base of the tank seems a little worn but still does its job. havent really gone too much further into the bike than this
another thing is that i can no longer let the bike idle without the choke on, or else it revs too low and dies.
this wasn't a gradual thing

thanks for your help !

[elevenhundred]

It could be your float bowls are not filling fast enough.
Are there any kinks in the fuel line from the tank to the carbs?
If you stop the bike for a few minutes then restart it does the problem go away (until it starts happening again of course)?
If you run the bike on the reserve setting does it do the same thing?

Does the problem occur regardless of whether the engine is hot or not?

[Squiggles]

try running it with the gas cap open

[el_scor_cho]

It could be your float bowls are not filling fast enough.
Are there any kinks in the fuel line from the tank to the carbs?
If you stop the bike for a few minutes then restart it does the problem go away (until it starts happening again of course)?
If you run the bike on the reserve setting does it do the same thing?

Does the problem occur regardless of whether the engine is hot or not?

fuel line seems fine, it seems to be 2 separate problems (idle problem and cutting out) that are linked somehow.

the bike will run all day in idle with the choke on, its not until i take it for a ride and give it a bit of gas that the problem occurs. if i ride it and this happens and the engine cuts out it wont start again for a good while; it seems that it has starved itself of gas and the lines became void of fuel, it will only startr up again if i a) manually squirt a bit of fuel down the lines or b) spend a while turning it over with the electric start.

the tap on either reserve or on doesn't seem to make a difference.

thanks

[el_scor_cho]

try running it with the gas cap open

the tanks has a breather valve that seems to be doing its job fine, will give it a go anyhow thanks

[el_scor_cho]

tried and checked all the above, any other input would be much appreciated

cheers

[Backmarker]

Try running the bike from another source, fuel container with gravity feed to the carbs via siphon for example. If you can make the bike experience the problem when sitting in neutral at higher rpm the job will be easier obviously.

Although I have been known to do a similar with an outboard tank strapped to the pillon seat.........

If the bike runs ok from another source then the tank/tap is the problem, if not may be time to have a look at carbs, great fun on a V4.....

[HenryDorsetCase]

hey guys need a bit of help.
my vfr 400cc (1989 nc30) runs fine for a while then seems to starve itself of gas after 5-10mins. almost exactly the same feeling as when the reserve switch on the tank is needed to be switched on. have taken apart the tank pipes etc and all seems to be in working order. although the diaphragm at the base of the tank seems a little worn but still does its job. havent really gone too much further into the bike than this
another thing is that i can no longer let the bike idle without the choke on, or else it revs too low and dies.
this wasn't a gradual thing

thanks for your help !

I had exactly the problem you describe. Unbelievably frustrating, and ruined a track day for me, and made me so angry.

In the end I had to get the bike on the dyno so the mechanic could replicate the fuel starvation problem. A lot of time, money and effort went into solving the problem (I did what you've done too: checked the breathers, pulled the fule taps apart and in fact took out the diapram so its "Free flow", yada yada yada. many hours and curse words, some money on mechanic 1, more money on mechanic 2 and the dyno time......

Know what it was? You will be amazed.
















(my flair for the dramatic there)....... drum roll please.




OK, check the hose that runs from the fuel tap to the fuel inlet manifold (where it branches into four feeds, one for each carb.) I replaced the bit of line when I was doing some maintenance, thinking it looked a bit tatty. I managed to cut the new fuel line about 40mm longer than the bit it replaced.

So when the tank is on the bike but not bolted down, it was fine, when you slid the tank into position and bolted it the fuel line crimped, restricting the flow. because its a straight shot from the tap across to the carbs it pushed the line forward and it crimped UNDER THE FUCKING CARBS WHERE YOU CANNOT SEE IT IS CRIMPED> So the thing gets full float bowls when you connect the fuel line, and then it gets restricted or stopped when the tank is bolted up. So it starts and runs and revs fine, then after a few laps runs out of gas. Take the tank off, look at everything, bolt it up again, same deal. runs for five minutes then stops. did I mention I found this incredibly frustrating and got very angry?

The most frustrating problem I have ever had, and fixed in literally ten seconds. I really appreciate the efforts of craig at Ashburton Honda who actually sorted it out.

bike runs like a top now. (also it has 59 hp.... not bad when it was rated 60 brand new 20 years ago)

[skidMark]

You know you have to put more in roughly every 220km's right?

[skidMark]

hey guys need a bit of help.
my vfr 400cc (1989 nc30) runs fine for a while then seems to starve itself of gas after 5-10mins. almost exactly the same feeling as when the reserve switch on the tank is needed to be switched on. have taken apart the tank pipes etc and all seems to be in working order. although the diaphragm at the base of the tank seems a little worn but still does its job. havent really gone too much further into the bike than this
another thing is that i can no longer let the bike idle without the choke on, or else it revs too low and dies.
this wasn't a gradual thing

thanks for your help !

On a more serious note, not enough gas is getting into the bowls ie its letting in just enough that it is running. but eventually it uses up the full bowls and is running on drips, i say it must have some going in or it would run out sooner.

My other thought would be wrong heat/ stuffed spark plugs that arn't coping when the engine gets up to temp.

[racefactory]

Henry Dorset is the man with the right idea here.

It's the fuel tap vacuum hose he's talking about. The little hose that comes off and attaches to the number 3 cylinder inlet manifold. (FUCKING hard to get to properly)


Have you already tried checking the breather hose that comes off the top of the tank? Or doing what squiggles said? Run it with fuel cap open? That's the other answer.


If the fuel tap vacuum hose is broken or disconnected then the fuel tap will close off. That hose ensures it is always open.

End of problem- surely. Good luck!

[vifferman]

It's the fuel tap vacuum hose he's talking about. The little hose that comes off and attaches to the number 3 cylinder inlet manifold. (FUCKING hard to get to properly)

Crapulence!
Does the VFR400 have these fookers too?
My old VF500 had one, and it was a pain. If it wasn't the hose getting perished and allowing extra air to get sucked into the cylinder, it was the tap diaphragm getting muntered and allowing extra fuel to get sucked in.
While I understand the philosophy behind vacuum-operated taps, in practice they're another unnecessary complication.

[el_scor_cho]

ok cool heaps of good idea to go on.
i spent the day ripping into the engine and got as far as being able to confirm that the fuel hoses aren't kinked and that the breather on the top of the tank is doing its job fine.
idling the bike without the tank bolted on doesn't seem to make a difference, still revs around 2k lower than it should with choke on full and cuts off when choke gets to around half way.
the vacuum hose seems to be in working order but the diaphram looks a little worn, could this affect it? or rather that it is an old-ish bike and the hose itself could be deteriorating? on the surface the hose and all the connections look tip top.

thanks for the suggestions; keep em coming

[el_scor_cho]

also does anyone know what part the vacuum connects to? is it a separate component that could have failed me mid-way through a ride?
will check the plugs also
ta

[lostinflyz]

is the idle screw set properly??? will it run on choke forever or does it die out eventually even with the choke on

Check the vacuum line as has been suggested. and check that the fuel pipe hasn't been replaced cause its jsut sooooo easy to make it too long.

The diaphram in the fuel tap on these can suck back into the outlet in the fuel tap if they are old and cut out fuel flow. i suggest you perform the modification to eliminate the diaphram all together.

Could be float heights but i would doubt it. Its definatly in the fuel line or tap. dont touch anything else until you are 199999% sure its not in the fuel or tap lines. Youll hate yourself for it.

Did the bike used to run sweet or is she a new purchase??