Duke 390 surging? - KTM Duke 390 Forum
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post #1 of 31 Unread 10-06-2019, 04:56 PM Thread Starter
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Duke 390 surging?

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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post #2 of 31 Unread 10-06-2019, 05:12 PM
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Duke 390 surging?

What do you mean by surging? What speed, what gear and how many revs when it happens?
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Last edited by Mirius; 10-06-2019 at 05:15 PM.
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post #3 of 31 Unread 10-06-2019, 05:32 PM
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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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Whatís a valve train?
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post #4 of 31 Unread 10-07-2019, 08:36 AM
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Quote:
Originally Posted by Whyzee View Post
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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post #5 of 31 Unread 10-07-2019, 10:01 AM
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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 thatís 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 itís civilised to dump additional emissions into the atmosphere.

Manufacturers donít appear to have ever believed itís a good idea else they would have done it back in the days before emissions regulations. They didnít because itís a bad idea. Riding at lows revs can damage the engine. Itís 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 donít see large singles much now and why the proposed 490 Duke is a twin.
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post #6 of 31 Unread 10-07-2019, 03:59 PM Thread Starter
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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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post #7 of 31 Unread 10-07-2019, 07:35 PM
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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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Whatís a valve train?
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post #8 of 31 Unread 10-07-2019, 11:49 PM
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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

As long as you are happy with what you ride.
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post #9 of 31 Unread 10-08-2019, 08:48 AM
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What runs excessively lean will soon be broken
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post #10 of 31 Unread 10-08-2019, 09:45 AM
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Correct, the 390, it does not my friend.

Quote:
Originally Posted by Whyzee View Post
What runs excessively lean will soon be broken
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As long as you are happy with what you ride.
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