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Engine Fluttering Sound

SergeantChuck

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Looking for some ideas.

The bike currently has 60K miles and recently started running strange. I would best compare it to a 8 cylinder running on 7 cylinders. When I'm below 3000 RPMs, the engine shutters a little and makes what I'd call a fluttering sound on acceleration. Above 3000 RPMs, it feels almost normal.

My first thought was a bad spark plug so I purchased two new EOM spark plugs and they have been replaced. My second thought was maybe a bad plug wire so closed the garage door and turned out the lights to look for an ark from the wires to some nearby metal. I saw no arks. I have checked the oil level and it is good. One thing I have not checked is the air filter but would not expect such a drastic change overnight from a dirty air filter. I could be wrong.

I'm starting to wonder if it is a slightly clogged fuel filter but looking for ideas now. This idea come to mind because a new fuel station got put in 5 block from my house and I started using this station. They offer non-ethanol fuel so I switched over. That could be a coincidence or not. I would rather not just throw parts at it and would like to see what the community has to say.

Thanks in advance. This is my daily driver so would really like to get her running good again.
 
As far as I know, the only fuel filter on the NC700 is at the fuel pump inside the tank, something not easily serviced.
 
As far as I know, the only fuel filter on the NC700 is at the fuel pump inside the tank, something not easily serviced.

Thanks, I was worried about that. I had not researched its location yet but had a bad feeling it might be there.
 
Thanks, I was worried about that. I had not researched its location yet but had a bad feeling it might be there.
A problem for sure. Does it do it when you roll on the throttle quickly or just any acceleration under 3000? What if you are above 3000 rpm and roll on the throttle hard/quickly? Fuel filter at 60,000 isn't a bad idea though. Is it a filter in the tank or a screen/sock?

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Rather than blindly replace parts( like most “auto technicians” nowadays), you could try some diagnosis. Have you done a compression test? Hooked it up to an oscilloscope to see if everything is firing correctly?
It does sound like an electrical gremlin, but bad injectors can mimic that too. Have you tried running a can of Seafoam through it yet?

HTH....
Let us know what you find!


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A problem for sure. Does it do it when you roll on the throttle quickly or just any acceleration under 3000? What if you are above 3000 rpm and roll on the throttle hard/quickly? Fuel filter at 60,000 isn't a bad idea though. Is it a filter in the tank or a screen/sock?

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Pretty much anytime I accelerate under 3000 rpm but it shutters a bit worse if I accelerate hard.
 
Rather than blindly replace parts( like most “auto technicians” nowadays), you could try some diagnosis. Have you done a compression test? Hooked it up to an oscilloscope to see if everything is firing correctly?
It does sound like an electrical gremlin, but bad injectors can mimic that too. Have you tried running a can of Seafoam through it yet?

HTH....
Let us know what you find!


Sent from my iPhone using Tapatalk

I have considered some form of "injector cleaner" but have not tried that yet. I have used seafoam on cars but never a motorcycle. I'm sure it couldn't hurt in small doses.
 
I have considered some form of "injector cleaner" but have not tried that yet. I have used seafoam on cars but never a motorcycle. I'm sure it couldn't hurt in small doses.
Mix according to the instructions. I have had very good results using AmsOil fuel cleaner when My daughter let her Rebel 250 sit to much for two years. It was given to her younger sister and I couldn't get it above 50 and I used to be able to get it up to 60-65 mph with my 6'3" bulk. Doubled the dose of cleaner in a batch of new gas. Went for a 70 mile ride. By the time I got back I was getting it to 60 on the level. Try a good cleaner. I use seafoam for storage in my bikes over the winter.

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Some time ago I fought a shuddering problem on a V6 minivan engine. It was subtle and only occurred when it shifted to overdrive at around 45 mph and the load was fairly high, in other words, a low RPM shudder. Over the course of probably two years I tried this and that, plugs, sensors, wires, even transmission treatments. In the end it was cured when I changed the coil pack. So while I’ve not heard of a bad ignition coil on an NC, keep way in the back of your mind that it could cause this.

Was the bike subject to a high pressure wash or a monsoon lately?

I don’t know if this thread fits your symptoms, but it’s worth noting. This one ended up being a bad fuel pump.

Engine Stuttering ??? Advice or Thoughts???
 
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Some time ago I fought a shuddering problem on a V6 minivan engine. It was subtle and only occurred when it shifted to overdrive at around 45 mph and the load was fairly high, in other words, a low RPM shudder. Over the course of probably two years I tried this and that, plugs, sensors, wires, even transmission treatments. In the end it was cured when I changed the coil pack. So while I’ve not heard of a bad ignition coil on an NC, keep way in the back of your mind that it could cause this.

Was the bike subject to a high pressure wash or a monsoon lately?

I don’t know if this thread fits your symptoms, but it’s worth noting. This one ended up being a bad fuel pump.

Engine Stuttering ??? Advice or Thoughts???

I rarely wash it so no on the pressure washing but it has been subject to rain. No high pressure rains though. She overheated on me twice yesterday when riding home which has two quick stops and I'm rolling about 50 mph the entire time. Here is a thought and would like to hear anyone's input. The last time I checked the valve clearance was about 20k miles ago. Could a valve out of adjustment cause this "fluttering/shuttering" and the overheating? I'm grasping at straws now but I'd rather solve this myself without taking it to the shop.
 
The valve check interval is 16k miles, so that service is due.
Overheating can be caused by low coolant level, stuck thermostat or bad water pump.
There has been a couple of cases where the timing chain jumped a tooth due to a bad cam chain tensioner. If that happened then the engine wouldn’t run quite right.
By checking the valves, you can verify the timing, set the valve clearances and flush the coolant. That hits all the main mechanical reasons for odd engine performance.

JT
 
Well, you can answer the valve question by simply doing a valve check/adjustment, so that’s easy.

I’m really puzzled about the overheating. Besides the cooling system causes that Jt105 mentioned, another thought I had is that engines burning lean mixtures run hotter. The lean burn would also explain the fluttering. But could possibly it run lean enough to overheat? That, I don’t know. What you could do is ride the bike awhile with the engine in the fluttering behavior, then stop, and pull the spark plugs and read their color. Are they stark white, like a lean burn? Are they both the same? They is a separate fuel injector for each cylinder.

Have you taken note if the gas mileage has changed since this problem arose?

Back on the idea about poor fuel delivery, it might also be worth the effort to measure the fuel rail pressure.
 
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There's a cooling fan behind the radiator. If the coolant goes above a certain temperature, the fan should start running and keep the engine from overheating. Does the fan start running?
 
So what would this above/below 3000 RPM condition be indicative of then?
In carbs it may mean the primary jet is clogged. In Fuel Injection I am not sure. If it was a filter then it would definitely bog down above 3000 as it would need more gas than at a lower rpm. Injectors just change the stroke length of the injector to change the amount of fuel injected. At least on diesels. What did your plugs look like when you pulled them out? Did they look white like you were burning lean? Check your valves as you are over the interval. Does it do it before it warms up to operating temperature? Injection does put more fuel in when cold. Is it colder where you are right now? Does it take some time to warm all the way up? If not then it could be an electrical device that needs to get hot before it acts up or when the engine gets warm the fuel system lowers the rich fuel mixture when hot and a weak fuel pump then reveals itself? Ask your dealer mechanic if they will put a fuel pressure gauge on it and let you go for a ride until it starts doing it. If that is ok then I would be suspicious of a coil and those can be tested too.

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There's a cooling fan behind the radiator. If the coolant goes above a certain temperature, the fan should start running and keep the engine from overheating. Does the fan start running?

The fan is working. I checked that after it overheated the first time.
 
In carbs it may mean the primary jet is clogged. In Fuel Injection I am not sure. If it was a filter then it would definitely bog down above 3000 as it would need more gas than at a lower rpm. Injectors just change the stroke length of the injector to change the amount of fuel injected. At least on diesels. I would pull the plugs to see if burning lean as suggested earlier. Then adjust your valves while you are there behind the radiator. Very interesting that it has to warm up and be operating at temperature. Injection does put more fuel in when cold. Is it colder where you are right now? Does it take 30 miles for it to warm all the way up? If not then it could be an electrical device that needs to get hot before it acts up or when the engine gets warm the fuel system lowers the rich fuel mixture when hot and a weak fuel pump then reveals itself. Pull the plugs. Ask your dealer mechanic if they will put a fuel pressure gauge on it and let you go for a ride until it starts doing it. If that is ok then I would be suspicious of a coil and those can be tested too.

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I think I still have the plugs I replaced and both plugs looked identical. What I mean is, one did not look like it had the side affects of a lean running system when the other looked normal. To me, nothing looked out of the ordinary on the original plugs. The symptoms occur immediately. Doesn't matter if the bike is hot or cold. I think the fluttering issues is still present above 3000 rpm but it is much less noticeable and acceleration is better.

There has been mention of loose grounds and such. I plan to look at those types of things today along with air filter since I'll be tearing into things.
 
My somewhat amateur thinking would also be pointing to a coil problem as is mentioned above. The misfire under load/acceleration has me thinking in that direction. However I have also seen poor running on my former KTM because of a clogged fuel injector. I have also previously seen fuel injector problems on here and that might turn up with a search.

I would doubt if it is a valve clearance problem and my thinking there is that the bike would not tickover properly due to poor compression becoming more of a factor at such low revs.

One other aspect to look at is tank venting.
 
I decided to check the air filter today. Keep in mind, it was supposed to have been changed by the dealer when I took it in for one last service prior to the end of my 4 year service package purchased from that dealer. That was at 48k miles and I am now at 60k. Air filter looked pretty crappy for only 12K miles since they "replaced" it. I just ordered a new one a few minutes ago.

Took a look at the ignition coil connections. They looked find. Still tossing around the idea of replacing the coils. They aren't too expensive.

20181124_102354.jpg
 
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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.
 
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