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Discussion Starter #1
I have roughly 1100 miles on my ‘17 Duke 390 and love the bike except the low speed surging. How can I eliminate that issue?
 

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We all have it. Some will tell you that it is the nature of a single cylinder motorcycle engine. Some will tell you it is your riding style, ie: not revving the snot out of the motor in a low gear to do 25-35 mph without the surging/lurching/kangarooing. None of that is civilized.

The fact of the matter is the air:fuel ratio is off. The engine EFI is programmed to run super lean in order to pass EPA emissions.

Buy and install a RapidBike Easy and all will be happy. 200$ and a simple installation.
 
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We all have it. Some will tell you that it is the nature of a single cylinder motorcycle engine. Some will tell you it is your riding style, ie: not revving the snot out of the motor in a low gear to do 25-35 mph without the surging/lurching/kangarooing. None of that is civilized.

The fact of the matter is the air:fuel ratio is off. The engine EFI is programmed to run super lean in order to pass EPA emissions.

Buy and install a RapidBike Easy and all will be happy. 200$ and a simple installation.
Yes. This. Or a Boosterplug - which I just got myself. Cheaper then the Rapid Bike and has a lot of the same science behind it.

$160 - delivered from Denmark in less then a full week. I got mine put on just this past friday night and whoooweeee what a difference.
 

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Sadly the laws of physics rarely care about civility. All new bikes run just as lean but only the singles run lumpy. But that’s no real surprise as they ran lumpy long before there were any EPA regulations.

Yes, you can smooth it out with an aftermarket fuelling device which will dump in more fuel. But the real question is whether that is really a good idea or not. Aside from whether it’s civilised to dump additional emissions into the atmosphere.

Manufacturers don’t appear to have ever believed it’s a good idea else they would have done it back in the days before emissions regulations. They didn’t because it’s a bad idea. Riding at lows revs can damage the engine. It’s even a problem with VTwins - any Harley rider ought to be aware of the dangers of lugging an engine - Harley specifically advise riders against it.

The problem becomes worse the larger the engine gets. There is a reason you don’t see large singles much now and why the proposed 490 Duke is a twin.
 

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Discussion Starter #6
I was told to just unplug the 02 sensor and will run much better but will have a check engine light on. It does this around 3k rpm.
 

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The stoichiometric air-fuel ratio (14.7:1) that is the ideal ratio for lowest emissions, but this isn't the best ratio for power. It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1.

I have had Honda XL 650 and KLR 650. Both are larger bore singles than the Duke 390. Neither ran lumpy but then again, neither ran as lean as the KTM 390

alconk don’t worry. You can fix your bike
 

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No comparison, both mentioned 650's produced about the same bhp as the 390 but at lower rpm's.
You don't need to fix what is not broken ;)
 

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Trolling again and trying to put the frighteners on new members?

Thousands of gen 2 390’s out there. No huge wave of broken engines despite being run for several years.

That said, I do have my doubts about the engine failure of Whiskey. But all bikes have some failures.
 

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I wholeheartedly disagree.
When an internal combustion engine runs excessively/extremely lean with an air to fuel ratio in the high 14’s it is borderline not running. Any leaner it will not run under load. Also it makes excessive heat! (Recall how some owners think the cure to fix their heating issue is a radiator cap with a higher pressure spring?).

When one simply corrects the air fuel ratio (richer in our case) and the engine runs smoother and cooler, it is a lean condition causing surging not gearing, riding style, rpm’s etc.

I promise that there is only one reason that manufacturers set these engines up so lean and that is to appease the EPA authorities

It takes a Troll to see a Troll.
 

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I have no business here as regarding trolls or not - what I can say is that I bought a used 390 two months or so ago that had 4200km on the clock. It was bought new in March 2019 by a friend that suddenly decided to upgrade to a bigger bike. I befriended the KTM dealer during a few visits there. I think the message I have heard is that the 390 is NOT a very durable motor... made NOT in Austria but in India mainly for that market. It DOES NOT fall in the class of the Austrian made Superduke R. (I know KTM claims it checks the quality before shipping - but what quality are we talking here?)



I have started a thread a while back asking about the mileage of current 390's... but this not being a very active forum (it seems) I got little feed back - most 390's having done not high mileage. I read all the positives and negatives of the 390 here. Apart from being informative I have picked up a lot of tricks & tips (a lot from you Mirius) - so by so that I have decided to do interim oil changes on the 390 as it seems to me that having so little oil in a reasonably high performing engine needs more frequent oil changes....


Whyzee I agree with the (too) lean running of the current engines - that we have to "thank" Germany's Merkel ... not only harming the engine, take away power but also making it "unpleasant" to ride in the lower rpm range...


So far I am satisfied with the 390... but watching it carefully (and I do have the remainder of the warranty in tact).
 

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Thank you Sir.
I also agree that you can do no harm in changing your oil more frequently than the manufacturer states.

I think Richard Cranium (Mirius) believes I am a troll simply because I disagree with his and others way of thinking (tuning). I don’t mind at all
 
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OK back to the OP ‘s question

Fit a Rapid Bike Easy, it’s a simple fuelling box that costs under UK£150 with only one wire to connect.
It makes the bike run SLIGHTLY richer (5% according to the manufacturer) than the standard settings.
It connects to the exhaust lambda probe and tells the ECU that it’s running a bit too lean.

Fitting this transforms the bike at low RPM. It will drive smoothly down to 5mph in first 10mph in second and 15mph in third without using the clutch.

The fuel economy on my bike went from an indicated 73mpg to around 68mpg.

But it’s so much nicer to ride. I think there’s another manufacturer who makes a similar unit

Note it’s not a tuning box so won’t increase the BHP.

My bike is currently on around 1200 miles and is a joy to ride in slow moving traffic compared to what it was like before.
 

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I think Richard Cranium (Mirius) believes I am a troll simply because I disagree with his and others way of thinking (tuning). I don’t mind at all

I have no issues with differences in opinion and I’m not in disagreement regarding lean running

I think you are a troll because you made fun of someone merely because they didn’t understand a technical term in English when it obviously wasn’t their first language. The resorting to name calling just underlines your trolling behaviour.
 

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lightning, you have changed your insurance then?

OK back to the OP ‘s question

Fit a Rapid Bike Easy, it’s a simple fuelling box that costs under UK£150 with only one wire to connect.
It makes the bike run SLIGHTLY richer (5% according to the manufacturer) than the standard settings.
It connects to the exhaust lambda probe and tells the ECU that it’s running a bit too lean.

Fitting this transforms the bike at low RPM. It will drive smoothly down to 5mph in first 10mph in second and 15mph in third without using the clutch.

The fuel economy on my bike went from an indicated 73mpg to around 68mpg.

But it’s so much nicer to ride. I think there’s another manufacturer who makes a similar unit

Note it’s not a tuning box so won’t increase the BHP.

My bike is currently on around 1200 miles and is a joy to ride in slow moving traffic compared to what it was like before.
 

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Sadly the laws of physics rarely care about civility. All new bikes run just as lean but only the singles run lumpy. But that’s no real surprise as they ran lumpy long before there were any EPA regulations.

Yes, you can smooth it out with an aftermarket fuelling device which will dump in more fuel. But the real question is whether that is really a good idea or not. Aside from whether it’s civilised to dump additional emissions into the atmosphere.

Manufacturers don’t appear to have ever believed it’s a good idea else they would have done it back in the days before emissions regulations. They didn’t because it’s a bad idea. Riding at lows revs can damage the engine. It’s even a problem with VTwins - any Harley rider ought to be aware of the dangers of lugging an engine - Harley specifically advise riders against it.

The problem becomes worse the larger the engine gets. There is a reason you don’t see large singles much now and why the proposed 490 Duke is a twin.
It only takes about 5% richer mixture to smooth out the bike.
That’s not what l would call “dumping” in extra fuel.
Eventually emissions regulations will kill off the internal combustion engine, but that’s the idea l guess if we are to become carbon zero.
 
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