Jump to content

NC750SD power loss and mpg drop


Marti

Recommended Posts

Hello.
First post here. Sorry for my English, not a native speaker.
So far the forum has been really useful, so thank you for that.
I could not find exact topic from older posts, so I had to make a new one.

The problem is this. About a month ago my bike (NC750SD '14) started behaving strangely. Fuel consumption increased by at least half a liter per 100km, noticeable loss of power when accelerating from 70-100kmh (bike vibrates, as if the brakes are on -they're not- especially in sixth gear, normally it's smooth as a sewing machine). Maybe it's something else but slight vibration/shake here and there while riding at steady speeds. BUT sometimes it all returns to normal mid-ride. No matter the weather, no matter the temperature. Longer trips, 170ish km at a time (commute to work).
Fairly new tires.
Changed oil and filters a few thousand km back. (Put in a little too much, pumped out after few trips)
New spark plugs (old ones had rather light-coloured soot? on them).
DCT reset (at first it seemed to help, but not for long - wishful thinking?).
Local technician recommended changing the fuel, because there have been problems with bad fuel lately. - No help.
I used Motul fuel system cleaner twice.
And now I'm here. Any ideas what could it be?
Something in the bottom of the fuel tank? Clogging the filter?
Battery? - I have no idea how old it (Yuasa) may be, but before longer rides I let it charge all night with a Noco smart charger. Starts fine.
Tested it after a long ride and bike standing outside for several hours today (6-8°C). 12.8V without ignition, 12.5Vish with ignition on, 14.45V at idle. The voltmeter wasn't fast enough to register the start-up drop but I think I saw a 10 or 11 smthng.
Some sensor?
Valve clearance?
Something else?
I would be very grateful for your thoughts.




Link to post
  • Replies 53
  • Created
  • Last Reply

Top Posters In This Topic

  • Jamesc

    8

  • davebike

    6

  • Steve Case

    6

  • Marti

    6

Top Posters In This Topic

Popular Posts

If it were mine or a customers I check / replace the Air cleaner add a alot of injector cleaner and giv it a dealers decoke (fast hard run)    

Sounds like a loose or corroded connector or fuse to me. Personally I doubt it’s fouled injectors because the plugs are both the same. I’d check the O2 sensor connections first, but I’d also look at t

Should no do so untill filter is really cloged or really free flowing taking the air flow past what the map can adjust for Visuly cheaking a air filter is a simple cheak and always called for wit

CO2 (lambda) sensor failing or poor connection maybe?

Link to post
SteveThackery
1 hour ago, Marti said:

(bike vibrates, as if the brakes are on -they're not- especially in sixth gear, normally it's smooth as a sewing machine

 

Ah, that might be a clue.  I suspect it's dropping back to one cylinder, which will cause the power loss and vibration.

 

1 hour ago, Marti said:

12.8V without ignition, 12.5Vish with ignition on, 14.45V at idle. The voltmeter wasn't fast enough to register the start-up drop but I think I saw a 10 or 11 smthng.

 

They sound fine.

 

There are lots of reasons why it could be intermittently running on one cylinder.  If it's worse at large throttle openings it could well be a problem with the ignition system (the higher the cylinder pressure, the higher the voltage needed to spark the plug).  I'd be checking the plugs, caps, HT leads, coils.  I guess it could perhaps be a faulty injector.

It's ages since I owned an NC, so I can't recall the specific details of the engine, but anyway, dropping to one cylinder is at least a possibility.

 

It is very difficult indeed to diagnose an intermittent fault via the Internet.  All you will get from us is a long list of guesses.  Really you need to diagnose the fault properly, in a logical way.  You might need test equipment.  Is there a competent motorcycle technician you could go to?

 

Link to post
outrunner

I would check the plug caps, my local bike shop has had a couple of older NC's with badly corroded caps.

 

Andy.

Link to post
14 hours ago, DaveM59 said:

CO2 (lambda) sensor failing or poor connection maybe?

 

Wouldn't this trigger a warning light?

 

14 hours ago, SteveThackery said:

 

Ah, that might be a clue.  I suspect it's dropping back to one cylinder, which will cause the power loss and vibration.

 

It is very difficult indeed to diagnose an intermittent fault via the Internet.  All you will get from us is a long list of guesses.  Really you need to diagnose the fault properly, in a logical way.  You might need test equipment.  Is there a competent motorcycle technician you could go to?

 

 

Yes, it is worth looking into. Felt some random shaking at lower speeds and constant throttle today. Also the idle is a bit jumpy right after starting. 

And yes, i'm afraid a proper technician should be the next step to make. But it was worth a try, sometimes the stupidest smallest things are to blame. 

 

13 hours ago, outrunner said:

I would check the plug caps, my local bike shop has had a couple of older NC's with badly corroded caps.

 

Andy.

The caps look like new. Must be something else. 

 

Thanks for your thoughts. 

Link to post

Warning lights will only trigger for permanent open circuits. Intermittent signals are usually put down to voltage variation and ignored. It's the only way when some analogue sensors are naturally noisy, you wouldn't want the ABS lamp latched every time you hit a bump in the road etc. 

 

Andy

Link to post

:welcome:

 

i was going to say contaminated fuel but noticed OP had mentioned that already. Looking at the newly installed spark plugs would give some idea if it could be on one injector or single cylinder running.

 

@Marti could it be the DCT at fault - wasn't there a chap on here recently with a high mileage NC exported from Netherlands...in Moscow i think he was but i can't find the thread again.

 

edit// Not Moscow it was Minsk, i was close :D thread below just in case it is any help:

DCT problems - Service Questions - The Honda NC Owners Forum (nc700.co.uk)

Edited by Jamesco
Link to post
Rocker66

Welcome to forum Marti. Sorry to read of your problems. As you will have seen those with more technical knowledge than me will be able to give you good advice. I hope that you find a cure for the problem soon.

Link to post

Running too rich for some reason. Should be straw colour.

Link to post

Thread here with some useful comments:

 

in the end it turned out to be dirty injector.

 

Strange that @Marti's old spark plugs were light & the new ones are now black, if they are the same heat range...unless the fault occured after changing the plugs?

 

 

Edited by Jamesco
Link to post

If it were mine or a customers I check / replace the Air cleaner add a alot of injector cleaner and giv it a dealers decoke (fast hard run)

 

 

  • Like 2
  • Thanks 1
Link to post
3 hours ago, Jamesco said:

Thread here with some useful comments:

 

in the end it turned out to be dirty injector.

 

Strange that @Marti's old spark plugs were light & the new ones are now black, if they are the same heat range...unless the fault occured after changing the plugs?

 

 

Thought the same. Guess it may depend on where it was run, motorway or town use?

Edited by MatBin
  • Like 1
Link to post
On 22/09/2021 at 08:57, Jamesco said:

Thread here with some useful comments:

 

 

Strange that @Marti's old spark plugs were light & the new ones are now black, if they are the same heat range...unless the fault occured after changing the plugs?

 

 

 

I used fuel system cleaner right prior to changing the spark plugs. Maybe thats why they were light?

 

And I mostly use it on motorway, long rides.

 

Today I had to go for a ride. The problem was still there, but sometime in the middle of the ride it suddenly disappeared for a while. I was riding behind a car at constant speed and felt a slight jerk.  Like something started to work, or freed up.  The power was there, no odd vibration while accelerating, fuel numbers dropped significantly.  I think it lasted until I had to make some faster manoeuvres and use more throttle. Maybe. To be honest, this has occurred before a few times - the problem goes away and then returns.  

Link to post

Sounds like a loose or corroded connector or fuse to me. Personally I doubt it’s fouled injectors because the plugs are both the same. I’d check the O2 sensor connections first, but I’d also look at the air filter/intake. 

  • Like 3
Link to post

@Marti I'd be surprised if the fuel cleaner completely cleaned the plugs, if it was added to the fuel tank only (assuming that the sequence of events was: fault occured, then fuel cleaner was added to tank & after the plugs changed).

 

An electrical/sensor fault is a good thought above, reasons for fouled plugs I can think of are 'only' wrong air-fuel ratio or weak spark; low compression also but the bike is usually running fine.

 

  • Like 1
Link to post
Quote

I doubt it’s fouled injectors because the plugs are both the same.

Why do you think that the NC series use a single injector for both cylinders

Link to post
1 hour ago, davebike said:

Why do you think that the NC series use a single injector for both cylinders

To save money.

Link to post
1 hour ago, davebike said:

Why do you think that the NC series use a single injector for both cylinders

Because twin throttle bodies have finally been identified as the pointless race bling and horror to balance they always were? 😁😈😁

 

This to me screams ignition trouble. A plug that never fires is frozen at the point it last did anything useful , so an intermittent problem with a coil or whatever will result in two plugs the same colour on a chop. 

 

On a CL or Brit bike the diagnostic can be done if you can get it to fail at idle (or want to get electricuted on the local bypass) . Pull off plug A it dies. Pull off plug cap B and nothing changes, ergo plug B was only there as decoration. I doubt this is possible on an NC. Maybe try a timing light pickup or one of those plug caps with a light built in? 

 

Andy

Link to post
SteveThackery
On 20/09/2021 at 23:40, trisaki said:

Valve clearance   

 

On 22/09/2021 at 05:43, Grumpy old man said:

Air filter?

 

Let's remember we are talking about an intermittent, and sudden, fault here.  I don't think either of those would cause the symptoms described.  

Link to post
Grumpy old man
24 minutes ago, SteveThackery said:

 

 

Let's remember we are talking about an intermittent, and sudden, fault here.  I don't think either of those would cause the symptoms described.  

On the modern fuel injected bikes would a clogged up air filter decrease mpg?

Link to post
Quote

On the modern fuel injected bikes would a clogged up air filter decrease mpg?

Should no do so untill filter is really cloged or really free flowing taking the air flow past what the map can adjust for

Visuly cheaking a air filter is a simple cheak and always called for with running issues I found pages from an AtoZ in filter housing causing massive rich running intermitently as they moved around (OK Carbed bike )

 

I think the hold thottle open to raise revs a few hundred and removing plug caps might help but very difficult to be sure withan intermitant fault I be cleaning caps and looking for splits / cracks first I also consider another set of plugs even if they have been changed but from a different sorce (there are copy ngk plugs out there )

  • Like 2
  • Thanks 1
Link to post
Steve Case

Excuse me for ignorance, I will chastise myself later. But there is only one intake port and one throttle body, is that correct?

 

Which along with the fact the gent said he changed the filters rules out fueling surely?

Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...