Rough engine when tank is near empty

It seems like all my problems are difficult to identify.

Since i had the bike (end of 2011), it was running rough now and then. It would idle perfect and always runs perfect when the throttle is opened 1/4 or more.
When i drive to my work in the morning, i have a 15km trip of slow traffic. Lots of schools, traffic lights etc. So i spend some time at speeds below 30km/h (under 20mph). After a while, it would sometimes start to feel as if it is fouling plugs. Slow or no throttle response, shaking, misfiring and not able to keep a steady speed when holding the throttle at a fixed position.
Last season, the problem seemed to be less (not gone) than the years before, but recently it came back. This time, i got a clue. Last season, i thought my reserve led was broken because i did not see it coming on for a long time. Seems like i just refilled too soon (my other bikes have a smaller action radius).
The past weeks, i refilled it a few times (waited every time for the light to come on) and i can see a clear pattern now. With a full tank, the bike is running as it should. No hesitation, no misfire, perfect throttle response.
As soon as the tank is half, it starts to run poorly again after a few miles in slow traffic. It gets a little worse when the tank is almost empty. When i enter the highway and open up the throttle, it takes up to 4-5 seconds for the engine to pick up and accelerate. When it finally does, and i have the possibility to pull it 2-3 times close to redline, the problem is gone. It will come back after a few miles of slow traffic.

You would not expect this behavior from a fuel injected bike. And i have no experience with injection systems, but does it sound familiar to someone?

I know my bike pretty good now. It is not a big problem as it would never die when doing this. But as a work-in-progress bike it would be nice to get it fixed.

Some details:
Tank has been replaced for the known leak 2 years ago. I don't remember it changing something.
Bike starts always good
I heard there are 2 types of ECU's. Mine is the early type.

It may be worth checking your tank breather for blockage or restriction

There are two small rubber pipes under the tank that serve as breathers

Try unlocking the fuel cap when you get the symptoms you describe and see if the problem goes away..? This would indicate a breather problem

I will!
I'll try to open up the fuel cap before every ride to see if it makes a difference.

I would assume a breather problem should have impact on large throttle openings also, but who knows. Cheap enough to check! ;-)

Dimitri,
You say that when this problem occurs, and then you get on the Highway, after a few runs up to the redline the bike runs normally until you slow down again.
Once on the highway, does the bike run OK even if the fuel level is low, or the tank is almost empty?
If so, and if the bike feels like it is ‘loading up’ in traffic, and at low speeds, first thing I would check is the spark plugs. They may be too cold. A cold plug will work fine under load on the highway, or at the redline, but will tend to foul or load-up at low speeds.
Have you changed the plugs lately, or has the bike been serviced recently?

Hello , I have just recently run out of gas on my 2014 Norton. I was going down the highway at 65 mph and it just died so I pulled over. The low fuel light had been on for a while , I thought I could make the next gas station . What I found was there was still some gas in the tank . I could see it kind of by the pump looking in, so I leaned the bike over towards the fuel pump and it started up again. So I ask those who have had their gas tanks off , or who have run them dry : Can we get to all of the gas in the tank or no ? I have not seen the bottom of the fuel tank , does it allow both sides of the tank gas to reach the fuel pump ? Also , How many gallons does it really hold ? Not 4.5 USG ? I was averaging 45 to 46 MPG US , but that was until I reached the magic 6000 rpm allowance. At this point the MPG drops especially with sustained high RPM operation. Also , I have seen the dreaded cable tie pinched vent lines running up to the fuel tank so I cut and replaced them. Those hoses are really too soft and small . I have found some good replacement for it . I am currently running it for the air box drain hose. Richard-7's Dad would be a great resource here. He has stretched many tanks on his trips.

Yes indeed. On highway speeds or idle it runs fine. Regardless of fuel level.

I did ask my dealer if it was fine to experiment with a hotter grade of plug. It was exactly what i had in mind. He told me going hotter up to 2 grades would not harm my engine. I never got to change them since because the problem seemed better.

Going hotter 1 grade would give a clue so i'll try that as soon as i have the chance to source a set locally. This would not clarify the influence of the fuel level either... but worth checking!


@Tony, when i fill it up, i never manage to fill up more than 13 liters (3.5 USG). The fuel light is on for at least 20km (13 miles) at that point. Mileage is about the same as yours (45/46 MPG) I don't spend a lot of time above 6000rpm.

Hello Dimitri , I think that 3.5 USG is going to be about all the gas we can reach . The 4.5 USG stated must be with the with the fuel pump removed ! And yes CR9EB is very cold (safe) , Try 8 range..

This may sound incredibly silly, but then again it may be the answer. I also can't check what I am saying because my Commando is 1973 vintage and I don't have access to a 961 workshop manual. I look through these postings because I drool over the 961, would like one, but my pockets are not deep enough, or if my pockets were, my wife would cut holes in them.

It's injected, the fuel must be in a 'rail' under pressure behind the injectors, pumped up to pressure by a pump, and the pump on a bike is often inside the petrol tank. It must be something to do with the level of petrol in the tank and the pump not being able continually scavenge the tank. Perhaps there is a tube in the tank that should lie along the bottom of the tank but has somehow moved so that the petrol ingress aperture is higher than it should be.

Just a long shot from someone who knows nothing.

Oooo ! It would therefore be running weak with a low fuel pressure which causes a 'hot' burn and with a 'hot' plug as well there is risk of unintentionally modifying your engine detrimentally. (can you tell that I once owned 2 strokes which have a habit of burning holes in pistons on weak mixture, early ignition or hot plugs)

With the tank low get a specialist to check the mixture on a rolling road, if you must put hotter plugs in. Just stick to standard recommended plugs, 4 strokes don't foul plugs like 2-strokes where there is oil in the fuel.

My fuel reserve light comes on solid when I have more than 1/4 tank, which I don't really mind because I'd hate to get stuck out there. What I do hate is the fuel light blinks a lot even when full. I'm going to address of of this after season, since last season was totally blown off with other issues. I really thing Norton owes some of us an extended warranty. If I brought it in now to address the oil leak from the crank case, the thwacking start up when cold and the blinking light, my warranty would be finished without any significant time on the road.

Britfan60 said:

My fuel reserve light comes on solid when I have more than 1/4 tank, which I don't really mind because I'd hate to get stuck out there. What I do hate is the fuel light blinks a lot even when full. I'm going to address of of this after season, since last season was totally blown off with other issues. I really thing Norton owes some of us an extended warranty. If I brought it in now to address the oil leak from the crank case, the thwacking start up when cold and the blinking light, my warranty would be finished without any significant time on the road.

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My low fuel light does not blink at all and comes on precisely 24 miles before empty, don't ask me how I know this! :lol:

Hello bphorseguy , How much fuel would you say the tank holds and how much fuel can we actually get to without running out , 3.5 gals ? The last time I checked my fuel mileage I got 48 mpg. I think 150 miles per tankful is safe. When I ran out my tripmeter read 153 miles . This was with lots of high speeds and aggressive acceleration . What mpg are you getting ?

I am getting 50-52 mpg and my fuel light comes on at 125 mi or so . I would say 3.5 gallons useable and 125 mi you should be looking for gas!

Britfan, does the blinking of your led occur when you're driving in the rain?

My complete instrument cluster will act strange when the bike is wet. Resetting the trip odometer (every time), warning lights burning without reason etc. But when dry it never does.

Funny how you get used to these stupid gremlins. First thing i do when leaving on a rainy day is is scrolling to the clock on the dashboard. Otherwise the odometer will reset.

Dimitri. No. I only rode in the rain one time to return the bike for repairs. It just blinks everytime I'm on it. Its more of an intermittent flicker. A minor annoyance. Crap, after what I've been through, who could actually take that seriously?