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Rich smelling exhaust nc700x


Tony Roche

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Tony Roche

Hi again guys. Having sorted my rough running problem by replacing a coil/HT lead, I've noticed when I'm stationery that the exhaust smells richer and I'm using more fuel. A mate who works on old bikes suggested a dodgy Lambda sensor and/or engine temperature sensor, both of which could affect the mixture. Anyone had this on an nc700x? Thanks guys

Tony

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Xactly

Not on an NC700 but I have had the same problem on a BMW oilhead. That one didn’t have a cat or, hence, Lambda sensor as it ran permanently open loop. Like your bike it stank of fuel and consumption was up dramatically. I removed the air intake temperature sensor and measured the resistance cold, then warmed it up in a pan of water (adding a little seasoning) and then measured the resistance again. It had barely changed. I was able to buy a used sensor on a sale or return basis and checked that in the same way. In this case there was a significant difference between cold and warm resistance. I therefore substituted the used one for the original and that resolved the issue. 
I assume that the engine warning light goes out after starting? If it doesn’t then it should be possible to decipher the fault code, something I’ve not yet had to do on my NC (a 750X) but have done successfully on other bikes.

I hope this helps.

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Tony Roche

Thanks mate that's very helpful info. My mate has been in touch again and told me about a "reset" procedure for the NC's after changing anything to do with the ignition or fuel system. It was posted by someone calling himself "Old Man"....... maybe from this forum????

1. Disconnect the battery

2. Turn ignition on and leave for a bit(I left it about 15 minutes to discharge any residual electricity)

3. Reconnect the battery

4. Start the bike by JUST pressing the button DO NOT TOUCH THE THROTTLE or anything else.

5. Leave to idle until the fan kicks in.

6. Hit the kill switch then turn ignition off.

 

I've just done this and the rich smell has gone, as has the occasional cough from the exhaust - though the bike was running ok. I'll run it over the next few days and post an update. 

Cheers Tony

 

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Cheesey69

Don’t the system adjust itself using the long term fuel trim?

if there is a fault then maybe all you have done is to reset this to base line. Over time I would expect the mix to become rich again. 
My experience is on cars but the system sees only the lamda sensor and only flag a fault if it goes beyond probable conditions 

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Tony Roche

Thanks for that. It does seem to be smelling a bit rich still but not as bad as it was. Fuel consumption is a bit high still I think. My local Honda dealer plugged it into their diagnostic today and there were no fault codes. They think that whilst it was running rough some unburnt fuel may have collected in the CAT or exhaust which will gradually burning off. If this is the case would the Lambda sensor be detecting this and affecting fuelling?? 

Cheers Tony

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Xactly

As cats run very hot I very much doubt that it would take long to burn off unburnt petrol, apart from which the O2 sensor is supposed to prevent rich mixture ruining the cat anyway.

 I don’t know about long term trimming dragging the mixture back to stoichmetric on these bikes but I would say that I doubt that the 02 sensor is wideband as found in modern cars but, like I say, I haven’t yet had any cause to look into the diagnostics on these bikes. If I get chance I’ll have a look at the W/shop manual to see if anything is said there. 
To test the dealer’s theory you could give it an Italian tune-up ie a bloody good thrashing. That should get rid of any unburnt fuel…..

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Tony Roche

Lol! Thanks for that. If fuel consumption remains high I'll try the air intake sensor......

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Tony Roche

I'm thinking that if either the Lambda sensor or the air intake sensor are faulty wouldn't this have generated a code?

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davebike

Yes should do !  look at air filter and look for debris in intake   Not got a stupid after market pipe on it many cause very rich low down and shit fuel echomany

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Cheesey69

Only throw out a code if improbable. Like way out otherwise how would it know it needs to adjust?

it’s not really a code it’s a reading but you need an in depth program. 
it’s one of a few sensors that won’t throw up a code unless seriously wrong, crankshaft sensor is another. 
what nearly always goes wrong with them is they get too slow to respond and the mix leans out and some systems that have an anti knock throw out a code because they can’t trim out knock 

if you think is the lamda then I would swap it out, they are cheaper than a diagnostic run. 

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Xactly

Had another thought: if what your dealer says is correct and the "rich" smell is occurring as a result of fuel residue being burned off the cat and/or exhaust, that implies that the the trouble is now resolved (or will be when it has all been burned off). In this case the spark plugs would look normal. If a problem still exists the plugs would be a bit sooty I would have thought. It's an easy check to remove the plugs to have a look. As davebike has said another possibility would be a bunged up (technical expression) air filter, though in this case the plugs would look sooty. I'd pop out the plugs and establish whether or not it's still running rich.

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Tony Roche

Thanks for your suggestions guys. The air filter was changed 15k miles ago (bike has done 48k). I think I'll take the plugs out over the weekend. I believe that my rough running caused by a dodgy HT lead/coil can foul the plug? I've yet to look at that plug. What's interesting is the bike is running sweet as a nut! I've filled up and am using the trip to check fuel consumption. Cheers Tony

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davebike

I would be changing an air filter that had done 15K if I has a fuling issue !

 

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SteveThackery
On 06/07/2021 at 16:00, Tony Roche said:

My mate has been in touch again and told me about a "reset" procedure for the NC's

 

Your mate is mistaken - there is no reset procedure for the NC ECU.  Check out the official Shop Manual if you find that hard to believe.

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Tony Roche

Morning guys and thanks for your further comments. I've run both my NC's the last 48 hours - yes I have 2 - and using the trip meter and fuel gauge consumption is virtually identical. The gauges are dropping within 3 miles of each other so I'm satisfied I don't have a fuel consumption problem. That just leaves me with a rich smelling exhaust! I'll check the plugs later. Maybe I just have a different cocktail of emissions coming out the back??

 

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Tony Roche

Hi again guys. So above are my plugs. The sootier one is from the side with the original coil/HT lead and the cleaner one is from the side where I recently replaced the coil/HT lead. To recap the situation, before I replaced the coil HT lead the bike was running rough. After replacing, the bike is running fine, fuel consumption is normal but I have a rich smelling exhaust. I'm not sure how to interpret this information so I appreciate your help! Is the sooty plug the cause of a problem or the sign of a problem?

Thanks guys

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Xactly

I’d say that there’s still a problem. It’s definitely running too rich on that cylinder. Clean the plug, ride the bike for a while and see if it’s still that sooty but I believe it will be. Maybe the coil/ht lead on that cylinder is on its way out too. You could probably swap them over to prove/disprove that.

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Steve Case

Do the NC still run a CDI to trigger the spark?

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Tony Roche

Thanks Xactly. I'm inclined to agree with you. I have another used coil/HT lead. I'm going to fit it and see what happens. Those plugs have done 8k miles. I'm thinking that if the lambda sensor and or air filter/intake sensor was faulty it would affect both plugs??

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Xactly

That’s my thinking, yes.

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Xactly

That’s my thinking, yes. You might want to check the plug gap too. It could be that the gap is too wide, weakening the spark.

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Tony Roche

Hi again guys. Thought I'd post a quick update. Air filter is clean as a whistle and the intake/temperature sensor is working. Resistance when cold is about 1800 ohms and 30 seconds with the hair dryer brought it down to 700. I've fitted the "new" coil but I can't remove the old one properly as the HT leads have those little clips attached which slide over lugs on the frame. Lowest one is easy to reach, second highest I did by undoing the radiator, but I have no idea where the highest one is! I can't even see it let alone unclip it. It's somewhere underneath the air filter housing which is attached to the intake on the engine...... obviously! Has anyone replaced the right hand coil before? Cheers Tony

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Tony Roche

Hi again guys..... quick update. I've fitted the "new" coil and been using the bike a couple of days....... it's still smelling rich. I'm going to fit a new lambda sensor as I can't think of anything else it could be.......apart from a dodgy ECU :-(

Will keep the post updated

Cheers Tony

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Chris750

ECU rarely go "dodgy" these days and as there are no fault codes relating to the lambda sensor it would suggest it's working within its range, looking at the picture of the plugs I would suggest you may have a leaking injector, may be worth running fuel system cleaner before throwing parts at it.

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