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 :wacko:

[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??

[lostinflyz]

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 :wacko:

i have had one of these with fuel starvation from a tiny wee pin hole in the vacuum line but it only did it sometimes.

[SHELRACING]

Must admit it sounds like a fuel issue, or vacuum leak. Most of which has been suggested.

Might be worth a look at the air filter if it's totaly farked or blocked. just a thought as a point of elimination.

Good luck

[Chrislost]

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 philosphy behind vacuum-operated taps, in practice they're another unnecessary complication.

just pull the tap apart, put the spring on the other side, and block all the holes...

[el_scor_cho]

kk i will have a good look at the vacuum tube line. fingers crossed it is only to do with the fuel lines.
bike is a recent purchase as of around a month ago now, i did however make it 4hours down south in the pouring rain where it then decided to give in for the first time. have done a decent amount of k's since purchase.
could the rain have tipped something over the edge possibly?

thanks for the ideas!

[racefactory]

also does anyone know what part the vacuum connects to?
will check the plugs also
ta

do you mean that shit is just dangling there free? That's your problem then.

The fuel tap vacuum line connects to the blanking stub on the number 3 cylinder intake manifold. The thing which you use to synchronize the carbies. Fuck it's hard to explain.... even with pictures. If you take a look at the metal part of the intake manifold on the rear right cylinder (number 3. It's really hard to see into there) , then you'll see a nipple and that is where it connects to.

[el_scor_cho]

oh an i dont mean its just dangling there, im sure i would have picked that up earlier.
just curious if anyone knows or heard of theses pumps giving in after a while

[RT527]

what about electrical...I had a cdi unt fail on me once , sought of produced roughly the same problems....just a thought is all.

what about sediment from your tank could that be blocking somewhere, also regulator rectifier probs.....are the spark plugs carboning up or is it running rich, check that the pilot screws haven't come off also check to see if the jets are right for your bike (sorry been a while since i had a vfr 400 , so cant remember the right settings)or that one of the jets isn't blocked or sticky.

[HenryDorsetCase]

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

check out this page.

http://www.akhara.com/nc30/fueltapmod/index.html

This is what I used when I got rid of the vacuum line altogether. Works like a charm.

Dont forget to crimp the vacuum hose off and tie it off as well.

My fuel tap now only has one line from it, to the carbs (i.e. gravity fed).

[HenryDorsetCase]

oh an i dont mean its just dangling there, im sure i would have picked that up earlier.
just curious if anyone knows or heard of theses pumps giving in after a while


"pumps" ? Fuel injected engines have pumps (or some designs where thefuel is lower than the carbs). Not your VFR though.

the fuel on a VFR400 is always gravity fed to the carbs. But the fuel tap won't flow unless there is intake vacuum. intake vacuum from (and I dont want to get into how a four stroke motor works, or discuss physics and shit... though when you were sitting in fifth form physics and thinking "Fucksakes, when I am I ever going to need to know this shit?". well, about now would be good..... I digress). OK, for the sake of illustration we will say that Mr Vacuum lives in the upstream side of a river we will call Mr Carburettor. When Mr Engine is running, Mr vaccum is free to visit his friend Mr Fuel tap, who lives in Petrol Tank City. When Mr Vacuum visits Mr Fuel Tap, Mr Fuel tap has to make room for Mr vacuum and he pulls up another chair we can call Mr Diaphram. That allows allows Mr Fuel Tap to allow his neices, the Petrols to visit their friends the Carburettors for tea and scones.


Or, the intake vacuum pulls a little rubber diaphram against a spring, and this allows fuel to flow.

But if you make the mod referred to above, you have taken out the stop (default option, no fuel flows) and fuel is free to adopt one of the three options on the label on the tap: Off means no fuel will flow, On means fuel will flow in the main open position and reserve means the other open position.

generally the issues with the vacuum system are the rubber parts: change out the hoses, diaphram and O rings.

[Backmarker]

There are a lot of good ideas here :yes:

The thing is to solve problems the best method is elimination, and the best principle is K.I.S.S Keep It Simple Stupid

The reason I suggested to run the bike from an alternate source is to eliminate the tank, tank pickup and vacuum shut-off as possible suspects.

I have a XT500 have a similar fault which ended up being a small piece of cellophane/plastic wrapping itself around the fuel pickup from time to time. We flushed the tank several times but the problem still persisted, then we ran the bike for two weeks from a tank off my TT and it ran fine, when we power flushed the tank with a 60psi pump catching the runoff through a strainer we found the culprit.

Also had a GSX250 doing the same thing, turned out to be a slightly burnt exhaust valve on the cylinder the take-off for the vacuum shut-off was on, with a burnt valve the manifold depression wasn't enough to consistently keep the fuel flowing for perfect combustion.

Eliminate all the basics first, one at a time so you notice any improvements/differences IMHO anyways

Cheers

[el_scor_cho]

Backmarker that's good advice thanks

spent the day tinkering again and bypasses the vacuum line and the diaphram with henry's method and it somewhat worked. the revs on idle have picked up and after a 10minute ride she seemed fine,
the only things that are still out of the ordinary is the fact that it dies when idling without the choke and it seems to not cope too well in low revs, that is when riding. accelerating in the low rev range it sputters very slightly, the bypass definitely helped a little

thanks

[SHELRACING]

Any chance you got water in the tank during that long trip. Is there a good seal around the fuel cap.

Backmarker has the right idea. Drain the entire fuel system. and start from scratch. Remove the tank and get hold of one of those little plastic minibike fuel tanks and run it off that.



kk i will have a good look at the vacuum tube line. fingers crossed it is only to do with the fuel lines.
bike is a recent purchase as of around a month ago now, i did however make it 4hours down south in the pouring rain where it then decided to give in for the first time. have done a decent amount of k's since purchase.
could the rain have tipped something over the edge possibly?

thanks for the ideas!

[racefactory]

Backmarker that's good advice thanks

spent the day tinkering again and bypasses the vacuum line and the diaphram with henry's method and it somewhat worked. the revs on idle have picked up and after a 10minute ride she seemed fine,
the only things that are still out of the ordinary is the fact that it dies when idling without the choke and it seems to not cope too well in low revs, that is when riding. accelerating in the low rev range it sputters very slightly, the bypass definitely helped a little

thanks

If it doesn't get better give it a carb balance. that makes it purr at idle. SHELLRACING could well be right about that water.

When you say idling without the choke- you mean when cold only? Is it idling low? have you tried giving the idle adjuster a little tweak?

[el_scor_cho]

ok cool ill try get my hands on an alternative fuel source today to try it out.

there's a very high chance water got into the fuel and the lines, i have drained the tank twice now to try and get rid of it all, is it possible water could have made its way further into the bike and still causing problems?

it idles low when cold and when hot, i could give the idle screw a tweak and im sure it would fix the idle problem but i want to avoid putting a bandaid on a potentially bigger problem

cheers

[Chrislost]

Backmarker that's good advice thanks

spent the day tinkering again and bypasses the vacuum line and the diaphram with henry's method and it somewhat worked. the revs on idle have picked up and after a 10minute ride she seemed fine,
the only things that are still out of the ordinary is the fact that it dies when idling without the choke and it seems to not cope too well in low revs, that is when riding. accelerating in the low rev range it sputters very slightly, the bypass definitely helped a little

thanks

what trademe said.
ballance the carbs...

spoon or two of meths in the petrol can help get water out...

[el_scor_cho]

a bit more to go on perhaps, i tinkered with a few things today like checking the choke slide and all the fuel lines again to no avail.

i got stranded at the bottom of my street again following this but found a few things that may help my cause. when the bike is in its funny 'cant get fuel' phase, and it is sitting in neutral, i gave it a rev and the revs were very slow to pick up , while the bike is in motion the engine sounds sluggish and slow compared to normal.
another thing is that when stationary, still in its phase of starving itself, and in first gear with the clutch in, if i rev it the bike lurches forward, the more revs the more the force forward. i know this sounds like the clutch isnt engaging but this does not happen when the bike is running fine

hope this triggers something
thanks for the help

[el_scor_cho]

also i heard through the grape vine that a disconnected speedo could result in some rather unusual behaviour as it slips into a 'safe mode' of sorts.
my speedo has been playing up lately especially after my latest long ride, anyone heard of such a case?

[skidMark]

a bit more to go on perhaps, i tinkered with a few things today like checking the choke slide and all the fuel lines again to no avail.

i got stranded at the bottom of my street again following this but found a few things that may help my cause. when the bike is in its funny 'cant get fuel' phase, and it is sitting in neutral, i gave it a rev and the revs were very slow to pick up , while the bike is in motion the engine sounds sluggish and slow compared to normal.
another thing is that when stationary, still in its phase of starving itself, and in first gear with the clutch in, if i rev it the bike lurches forward, the more revs the more the force forward. i know this sounds like the clutch isnt engaging but this does not happen when the bike is running fine

hope this triggers something
thanks for the help

its a seperate issue, adjust your clutch.

[el_scor_cho]

for anyone whos interested in an end result it seems the problem was the fuel tap.
althouh i checked it and seemed to be flowing fine it was aparantely not right. so if you have the same problem make sure the fuel tap is working properly and flowing freely.