Hi all,

I cannot get my VFR400 NC24 firing on all four cylinders. It runs fine on front two but will not fire on the rear two rears. I have tried two sets of carbs one ultrasonically cleaned and still no joy. I have been trying to get it to run for weeks so far I have performed the following with no benefit gained:

1. Compression check- rear cylinder compression rating same as friont cylinders so all good there.

2. Sparks good on all cylinders- swapped front to rears just to rule out dodgy plugs but still no joy.

3. Two sets of carbs fitted and tried (one had been ultrasonically cleaned). The second set I used the ''drill bit method'' just to get a rough balance to try and get the bike to fire on all four. Still no joy.

Am I overlooking something stupid, would running the bike without the air box setup and pipes on cause the rear cyliders not to fire???

Any advice welcomed as this is stretching my patience.

The bike will run totally tits without the airbox.

Put the airbox on.

Full choke, no throttle until it fires. Warm it up for 30 seconds and all four should be firing.

The floats take a while to fill up due to the vaccum tap. (if your not using it make sure you have blcoked the vaccum line else you will have air leak)

crack the drain screw to make sure you have fuel in all the float bowls.

I take it you checked for spark on the rear plugs?

Thanks for the advice. I will re-fit airbox and re-try this afternoon. I will have everything crossed

On the subject of the air box one connection, one tube feeds into the coolant header tank but I have one spare tube(front one) spare where does this connect?? I have two feed tubes from the carbs one thin tube, which I have been fitting to the vacuum tap and the other larger goes to the fuel feed. Is this correct? At the moment after everyhing is fitted and hooked I still have a spare feed tube from the airbox and I don't know where it connects?

fasttom wrote:I have two feed tubes from the carbs one thin tube, which I have been fitting to the vacuum tap and the other larger goes to the fuel feed. Is this correct? At the moment after everyhing is fitted and hooked I still have a spare feed tube from the airbox and I don't know where it connects?

The small vacuum hose from the fuel tap fits onto a spigot on the L/H rear cylinder. It's quite difficult to see behind the frame. The tap end fits to the spigot on the side of the tap, not the rear one - that is left open.

There should be a loose hose from the airbox, it's the overflow and routes down by the shock.

right I am confused , which is easily done. There are three feeds from the fuel tap. Large one which goes directly to carbs to supply fuel feed. When I bought the bike the small thin tube from the carbs was attached to the horizontal feed from the fuel tap. The small vertical feed from the fuel tap was not connected to anything. There was no tube running from the spigot on the left hand rear cylinder, where does this feed attatch?

Help gratefully received.

The spigot on the left hand (right hand as you sit on the bike I think) rear cylinder should be attached to the tube coming from the spigot facing the same way as the fuel feed on the tap

The horizontal small spigot on the side of the fuel tap should have a hose attached which fits to the spigot on the side of the left rear cylinder, it should not go to the carbs. It uses vacuum provided by turning the engine over to pull the diaphragm inside the tap to open it The spigot on the rear of the fuel tap is left open, it's a breather/balancer.

So where does the thin tube from carbs route then, as currently this is routed anbd connected to the horizontal spigot on fuel tap?? bike was like this when I bought it Currently fuel tube from tap is connected to feed on carbs which is correct and thin tube from carbs to horizontal spigot on fuel tap. Air box is fed to cooolant header tank and front end left free (unconnected). I have no cennection to rear cylinder spigot at all

The thin tube should not be fitted to the carbs at all but the vacuum spigot on the left rear cylinder. The spigot on the carbs should be blanked off. A pic of exactly where it is connected to the carbs would help though

So am I right in thinking that there should be a tube from carbs that remains unconnected and only the main fuel feed hooked up to the carbs?

Presumably there then needs to be a tube ran from the horizontal spigot on fuel tap to spigot on left hand cylinder?? The bike was not hooked up like this when I bought it which may explain why I still can't get the rear cylinders to fire!