Engine Fluttering Sound

[SergeantChuck]

That air filter looks pretty bad. I would almost bet it got missed. Is the center oily ? Is the oil level correct? Too high a level can do this. One reason to look into servicing your bikes yourself.

Oil level is good. I changed the oil myself the last time two times since my warranty ran out and the oil was one of the first things I checked when the problem began. I was looking to see if the oil level had raised and antifreeze level had lowered. I have a feeling the filter is the original so it has 60K of debris.

 

[b_rubenstein]

The dark area is in line with the intake snorkel in the airbox so it gets a direct stream on intake air. It has nothing to do with the oil level in the engine.

 

[SergeantChuck]

Update on my situation. The problem has not been resolved but I figured I would list what I have done so far for historical and future troubleshooting purposes.

1. Checked Oil Level
2. Replaced Spark Plugs
3. Replaced Air Filter
4. 3 X Tank of fuel with Seafoam
5. 1 X Tank of fuel with HEAT
6. Replaced Ignition Coils
7. Opened fuel cap while riding to test venting
8. Checked for loose ground wires.

Thinking about checking for a small vacuum. In the old days I would just spray carb cleaners around hoses and listen for a difference in the idle. Any suggestions on how to do that with a bike? Same way?

 

[Jt105]

Good idea. I think it would work to spray around the intake. It could be a loose or cracked vacuum seal somewhere.
Makes as much sense as anything.

JT

 

[rippin209]

I had a similar problem when I serviced my K&N filter I used a aerosol spray that was supposed to be designed for cleaning my O2 sensor that's located inside the air box (the one you have to disconnect when changing/servicing the air filter)
because I was messing around that area when I started having problems (which was almost immediately) I figured it was the O2 sensor,
I ordered a new one, installed it and did the reset buy disconnecting the battery, turning the key on to discharge anything in the system, let it sit for awhile then hooked the battery back up turned on the key, started the motorcycle and didn't touch the throttle at all until after the fan came on (full operating temp) sure enough my motorcycle ran perfect after that.

I did ride my NC for almost a week (around 500 miles with it not running perfectly)
After all that, a week or two later my water temp sensor (controls the radiator fan want bad) my NC had 65k/66k miles when this all happened. Changed the water temp sensor and my coolant and my NC us back to normal.

Good luck, I hope that was helpful

 

[670cc]

Regarding a possible vacuum leak, I’m posting this is as food for thought, nothing else.

On carbureted motorcycles, you have the carb mixing fuel with the air, then the flow typically passes through a boot to the cylinder head. Any vacuum leaks downstream of the carb introduces more air and leans the mixture. On the NC , the throttle body controls air flow. But, the fuel is injected in the head, just before the intake valves. A leak at the throttle body boot could mess up the accuracy of the computer’s feedback as to how much air is actually entering the engine, but it’s less likely it could lean the mixture on this engine. In closed loop mode the O2 sensor feedback in the exhaust would induce fuel trim to put the mixture back where it should be.

 

[SergeantChuck]

Just an update. The problem still has not been resolved. I have added something new to the list of troubleshooting steps.

1. Checked Oil Level
2. Replaced Spark Plugs
3. Replaced Air Filter
4. Replaced Ignition Coils
5. Opened fuel cap while riding to test venting
6. Checked for loose ground wires.
7. Mass air flow sensor
8. 3 X Tank of fuel with Seafoam
9. 1 X Tank of fuel with HEAT

The last thing I tried was replacing the mass air flow sensor. Why the mass air flow sensor you might ask? The bike seems to be running a little lean on one cylinder so questioning the air fuel mixture plus I rode home in the pouring rain last week and the bike ran its worst since the problems began. This sparked the idea of either an exposed wire against the metal and the wetness worsened the problem or the mass air flow sensor because I had read of "wet/humid air" causing this affect with a bad sensor. I have ridden the bike 60 miles after changing the sensor and it felt a little better but nothing drastic. Probably just my imagination. I believe there is a cycle the ECM goes through and doesn't necessarily provide new readings immediately which would adjust the air fuel mixture so I will ride a few more days but not real hopeful that it will change things.

I ran into a mechanic friend the other day that is well versed in bike repair. He mentioned that he has dealt with fluttering issues in the past and it was normally two things. A very carboned up throttle body that was not allowing the butterflies to shut fully and a bad ignition module. He said stator but he has never worked on a NC700 and he assumes it does not have a stator but has an ignition module which I confirmed and have found one to purchase.

He recommended I first clean the throttle body, then buy the ignition ignitor module if that does not work. This will be my next step.

 

[davidc83]

If the bike is overheating, has anyone suggested replacing the thermostat? Malfunctioning thermostats can cause all kinds of problems (not just overheating)....

 

[b_rubenstein]

The bike seems to be running a little lean on one cylinder so questioning the air fuel mixture...

The bike has a single throttle body and a bifurcated intake port in the head, so both cylinders receive the same air/fuel ratio.

 

[SergeantChuck]

If the bike is overheating, has anyone suggested replacing the thermostat? Malfunctioning thermostats can cause all kinds of problems (not just overheating)....

No longer having an issue with overheating. So far.

 

[SergeantChuck]

The bike has a single throttle body and a bifurcated intake port in the head, so both cylinders receive the same air/fuel ratio.

Yea, I have removed the filter housing from the throttle body a couple times but didn't focus any attention on the cleanliness or lack of cleanliness. I was changing the coils. I think my CBRs had four throttle bodies but knew there was only one on this bike.

 

[Junkie]

The bike has a single throttle body and a bifurcated intake port in the head, so both cylinders receive the same air/fuel ratio.

They should, but injector spray patterns aren't always perfect. It's possible that it's partially clogged and spraying more in one direction than the other.

 

[670cc]

The bike has a single throttle body and a bifurcated intake port in the head, so both cylinders receive the same air/fuel ratio.

I have to disagree. Referencing the cut-away photo of the NC700 engine in post #28, the engine has two fuel injectors, each situated above an individual intake path to it’s corresponding cylinder’s intake valves. While the FI system does not likely send different signals to each injector, a failure or partial failure of either injector could result in the cylinders receiving different air/fuel ratios.

 

[Junkie]

You say you replaced the coils. Did you replace the plug wires with them?

 

[SergeantChuck]

You say you replaced the coils. Did you replace the plug wires with them?

Yes. It was a PITA to get them free but I replaced both.

 

[SergeantChuck]

I just got the air box out and the throttle body is now exposed. I was surprised to see that the throttle body is really loose. I could spin it freely from left to right with no resistance. I expected the bottom clamp to be tighter than that. Cleaning the throttle body may not fix it but it can't hurt. Since I am removing the throttle body for cleaning, it might be a good time to think about replacing the fuel rail and injectors since they are directly behind the throttle body. The only bad thing about doing two things at once is you don't know which one solved the issue. Wishful thinking on my part.

 

[Junkie]

Yes. It was a PITA to get them free but I replaced both.

I'd think that if you replaced both, you wouldn't have had to get them free.

If the TB is that loose you may have a vacuum leak.

 

[670cc]

I just got the air box out and the throttle body is now exposed. I was surprised to see that the throttle body is really loose. I could spin it freely from left to right with no resistance. I expected the bottom clamp to be tighter than that. Cleaning the throttle body may not fix it but it can't hurt. Since I am removing the throttle body for cleaning, it might be a good time to think about replacing the fuel rail and injectors since they are directly behind the throttle body. The only bad thing about doing two things at once is you don't know which one solved the issue. Wishful thinking on my part.

A loose throttle body is unexpected on an NC. They should have put the oil filter guy on that job.

If the price of new injectors irks you, I do have a set of used ones around I could part with. They were removed from beemerphile’s NC at 30k miles, but they must be good because replacing them had no effect on the engine.

 

[rippin209]

Hearing that the throttle body was loose is an odd problem but explains the symptoms. I remember reading this thread awhile back and recently had similar problems.
No noticeable power loss but it felt like riding something with a carburetor with the choke on our when it's cold.
Not noticeable (at least to me) at an idle or when above 4,000 rpm but under load (when riding) it was definitely not right.
I thought bad gas or a vacuum leak so I take out the air filter and there's a small gasket on both the top half and bottom half of the air box and part of it was out of place, lined it all up put it back together (did the EFI reset) and sure enough problem is gone.

It doesn't take much to make a noticeable difference on the NC apparently

 

[MZ5]

Intake tract leak could easily swamp the ECU's demand (control) authority to adjust pulse width on the injectors.