vfr 400 nc30 not getting gas

[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

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

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...