Fuel

[Robbo]

Hi have a 2015 nc750x with 60, 000 miles on clock.
Have an issue with fuel gauge.
On 2 bars starts flashing to fill up but has still 3 litres in tank.
Recently when it gets down to 2bars will not start as if no fuel, fill up and its starts ok. Any ideas
Cheers Dave

 

[CamaroEric]

If I recall normal reserve would be about 2.5l. At 60,000 miles, you're probably due to check the fuel pump and filter/strainer. It could just be clogged and starving for fuel that low. All just best guesses though.

 

[670cc]

I think a little more information is needed to assess whether the gauge is working properly. For example, is the fuel gauge behaving normally at the full level, and does the first fuel bar drop off at the expected distance traveled? And, from the point where the flashing gauge bar comes on, does it take the normal amount of fuel to refill it? When you have a no start condition, how much fuel does it take to fill the tank completely to the neck of the tank?

You said, “On 2 bars starts flashing to fill up but has still 3 litres in tank.” How do you know how much fuel is actually remaining in the tank?

The fuel pump is in the tank and the pickup screen is fixed at the bottom of the tank. For it to not pickup fuel at only a low level would meen the pump assembly/pickup screen has become dislodged from it’s mounting position, which seems possible but unlikely.

A possibility you might explore is whether the tank venting is compromised. What if, when the fuel l gets low, the tank has a strong vacuum in it because it is not properly vented? This can certainly be a problem in a gravity flow fuel system, but I don’t know if it is possible with a pump pressurized fuel system. When the bike won’t start, does temporarily opening the fuel tank cap make any difference?

 

[lootzyan]

You need to check the fuel level sensor. And to do that you have to remove the fuel pump. You need a service manual for your motorcycle model that has fairly detailed instructions on what to do.
Here is an example for NC/CTX700 models:

 

[DSLEMKE3]

On my 2015 NC700X with 8400 mi.:
After running out of gas twice in a just a few months when the fuel gauge was still indicating 2 bars, I decided didn't want to rely strictly on the tripmeter to determine my next fuel stop. I took a few hours to disassemble most of the back 1/2 of the motorcycle (I've got saddlebags and a trunk) so I could remove the fuel tank and inspect the sending unit and float arm. My suspicion was that maybe I had inserted the fuel nozzle at a gas station too far at some point and perhaps bent the float arm down causing the fuel gauge to read artificially high even though the float arm was at the bottom of its travel (although once I had the tank out I could see that it would be virtually impossible to reach that far into the tank with a fuel nozzle). My next check was verifying the resistance values from the sending unit. I found that at the full level my sending unit was in spec at about 5.3 ohms. However... at the bottom of float arm travel the resistance only reached around 74 ohms. According to the service manual excerpt from lootzyan above, 80-83 ohms is expected. I'm currently working with American Honda Powersports to procure a new fuel pump / sending unit assembly at their expense even though I'm well out of warranty. I'm convinced this is not a normal wear item and should have been accurate for the life of the machine.

Looking back at my troubleshooting steps, if I could do the whole thing over again, I would have started by verifying fuel sender resistance at the connecter on the back of the gauge/cluster. It's a simple matter to remove the windshield to get to the cluster, remove the connector and check the appropriate 2 pins (Black/green tracer and Green/red tracer) in the corner. This additionally verifies all wiring and connection points along the way and tells you what the gauge is really seeing.

Interesting tidbit... on the first out of fuel occurrence I was actually watching the tripmeter very closely and wondering why I hadn't seen the gauge drop to the normal flashing single red bar at the bottom because I knew I was getting close to being out. I was at 272.2 mi when the fuel pump finally starved and the engine died. I had been averaging around 72-73mpg on that tank but I was still surprised I made it that far. Mileage was not as good on the 2nd occurrence and it died at around 259 mi. Previously I had a 2012 NC700X with around 20K miles that I regularly averaged 76-77mpg on my conservative 16 mile commute to work. These machines are efficient if nothing else!

I'm new to the forum and actually found it while I was in troubleshooting mode on this incident. Perhaps my experience and details above will similarly help someone else down the road. I appreciate all the information I found here in various threads!

​

 

[Ozzieflyer]

Does anyone use fuel system cleaner additives to assist with keeping your fuel tanks and maybe the filters clean on your bikes?

 

[potter0o]

I have used an injector cleaner a few times in 9 years of ownership. Nothing scheduled. More random when I was thinking about keeping the injectors clean. I never had any indicators it was necessary/required.

 

[TXBootScoot]

I have used it a injector cleaner a few times 9 years of ownership. Nothing scheduled. More random when I was thinking about keeping the injectors clean. I never had any indicators it was necessary/required.

Which cleaner additive did you use? Any specific brand?

 

[potter0o]

Which cleaner additive did you use? Any specific brand?

It is the house brand of a national chain in Canada. It is the same stuff I used for past vehicles. I just changed the serving size to what I felt was appropriate for the different sized fuel tank.

Not sure if the link to the product will work for the US but it can be tried below.
Canadian Tire

 

[670cc]

Does anyone use fuel system cleaner additives to assist with keeping your fuel tanks and maybe the filters clean on you bikes?

No. I have not found that fuel additives are necessary.

 

[the Ferret]

Does anyone use fuel system cleaner additives to assist with keeping your fuel tanks and maybe the filters clean on you bikes?

I pour in a little Seafoam occasionally.

 

[Dan German]

A possibility you might explore is whether the tank venting is compromised. What if, when the fuel l gets low, the tank has a strong vacuum in it because it is not properly vented? This can certainly be a problem in a gravity flow fuel system, but I don’t know if it is possible with a pump pressurized fuel system. When the bike won’t start, does temporarily opening the fuel tank cap make any difference?

This needs to be checked for sure. We had an NC750 come into the shop with a venting issue that caused the tank to cave in.

 

[Ozzieflyer]

I had an issue where the acceleration would stutter at about 4,000 rpm occasionally a few years ago. I put in some injector cleaner the next tank and never had it again. Maybe coincidence but just glad it has gone.