Hi all

I have a NC35 tracky, which has a slight fueling problem. The bike has a full system, open air box and larger main jets. The problem only occurs when the fuel is low, the bike loses its top end and makes rather unsettling rattling noises (sounds like its pinging coz not enough fuel is getting in). It does however run very well when the fuel is topped up (at a guess more than half a tank). Has anyone experienced this before, and would anyone have any potential solution.

Thanks, Eden.

have you checked to see if the tank has any rust/gunk in it?

This is the kind of setup that would beneift from the HRC tap mod - it might be starving itself on prolonged open throttle.

I assume that the bike does not starve when on WOT for only a few seconds, but rather when at high revs for a good few seconds down sraights?

banoffee wrote:have you checked to see if the tank has any rust/gunk in it?

I have not, I will have a look, but how would rust/gunk only effect the fueling when the tank is low?

CMSMJ1 wrote:This is the kind of setup that would beneift from the HRC tap mod - it might be starving itself on prolonged open throttle.

I assume that the bike does not starve when on WOT for only a few seconds, but rather when at high revs for a good few seconds down sraights?

The bike doesnt stave when the tank is above half full, even down the straight in WOT in high revs. The problem comes up when the fuel gets a bit low (guessing less than half a tank), and it occurs every throttle position. Its directly related to the amount of fuel in the tank, because I get back to the pits, turn the bike off, fill it up and it runs perfect again. It is rather strange really.

I recall Steve / vfrman used to have an issue similar to this - starvation in corners. All I can imagine is that the physics of the fluid from the tank to the floats - perhaps there is not enough height of fluid drop to create the pressure required to kep the float bowls full? I imagine the fuel is pressured into the bowls rather than sucked in so perhaps a fuel pump would help?

Are you running on "reserve" or "on" positon?

eden.kwok wrote:how would rust/gunk only effect the fueling when the tank is low?

it might if floats...

CMSMJ1 wrote:I recall Steve / vfrman used to have an issue similar to this - starvation in corners. All I can imagine is that the physics of the fluid from the tank to the floats - perhaps there is not enough height of fluid drop to create the pressure required to kep the float bowls full? I imagine the fuel is pressured into the bowls rather than sucked in so perhaps a fuel pump would help?

Are you running on "reserve" or "on" positon?

There are no markings, but I am turning the tap down. A fuel pump does make sense, however I really dont want to run the risk of running the bike when no fuel is getting to the cylinders. Its rather worrying to be honest, its only happened three times and i just limp it into the pits with barely any throttle and refuel.

With some set ups a gravity feed isn't good enough and a fuel pump is needed. Best bet is to seek out a rvf tracker that has a similar set up to compare! Otherwise check all vacuum hoses especially the one from the tank(hole inside fuel cap!)

My race bike has always done this, I make sure the tank is over half full and I don't get any problems.

Other racers I talk to with open airboxes have the same issue, you can get around it by filling the tank over half full or using a fuel pump.

Does it have the hrc fuel tap mod? You'll need it if you run an open airbox as there isn't enough vacuum present at all times to use the standard vacuum operated fuel tap.

Check to see that the fuel is turned to on (full anti-clockwise), and that the fuel breather is working properly on top of the tank.

It's easiest for me to just keep the tank topped up.