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Jerking Issue

30K views 42 replies 26 participants last post by  Mirius 
#1 ·
Hi, I have completed 1200 km on my new KTM Duke 390 model and first service is done. I am facing a issue from the day one but the service guy says it's common in a high capacity single cylinder motorcycle. The problem is the bike jerks in low rpm, below 3000 - 3,500 rpm even in first gear. The feeling is like that the fuel is not coming to the engine but the problem disappears in high rpm. No problem in open road or highway. But it is irritating if I ride in traffic in slow speed. Is it the characteristic of Duke 390 or a problem with my bike ?
 
#7 ·
This is also often referred to as lean surge... the bikes run very lean. The Akrapovic map will help some as will a PCV or Bazzaz etc.
 
#8 ·
390's just run super lean man. Aside from getting a fuel controller to richen up the low rpm fuel mapping, you could also get a G2 quick action throttle tube to help you adjust to opening up the throttle faster and not sitting in low rpms. Plus side is it will help you develop better throttle control since you'll be up higher in the rpm's and with a more sensitive throttle. :)
 
#10 ·
Same here, but I already knew that it would do it. When I am splitting traffic, I chuck it in 3rd gear and cruise at about 35-40 kph (about 25 mph). This is about 4000rpm. Helps a bit because the torque curve is reduced due to the higher gear so you don't get the jerk as much when the ECU pumps more fuel in. Could probably cruise in 4th at that speed, but the throttle response is no good if you need to get out of trouble.
 
#11 ·
I have the issue in 1st gear as well, the same was for my Honda Ruckus which is a single cylinder as well. It wasn't so much from being lean, it's just the nature of the motor. My ruckus was tuned perfectly using a wideband. (that doesn't mean it won't help, but it won't remove the problem completely.)
 
#15 ·
Another option is "Tamer Throttle Tube" from G2ergo. Mine was part # 40-4H-HYK.
Labelled for several Honda and Kaw models, but rep told me it would fit the Duke 390. He
was right.

And it eliminated about 98 % of the lean surge and driveline snatch. Recommend it highly!
What a difference. I can ride now at 3500 in top gear without feeling as though I'm going
to get bucked off. Actually don't very much, as the engine vibrates more there. But it can
be done.

Cheers, John
 
#17 ·
Is this the opposite of quick action tube?
Someone else mentioned?
Seems quick action would make more jurky but claimed otherwise!
Regardless it seems to be lack of fuel for emissions causing it, different throttle tubes are just masking issues.
Akra remap or fuel controls fix issues very well .
 
#22 ·
The PowerTRONIC would eliminate (or reduce to a considerable extent) the jerkiness that several 390 owners face due to it's ignition and fuel control algorithms aside from the maps that we provide. With hours of research put in on the dyno and on road, we have optimised our algorithms and identified that even on similar maps the PowerTRONIC would perform par excellence.
 
#23 ·
Just to add to this in case anybody finds the thread on a google search.
I had this issue on my 2019 Duke 390 and pretty much eliminated it by fitting a “Rapid Bike Easy” unit.
I am sure there are other similar devices available but this was the cheapest and came up on a search for this bike.

There is a better version called the “Evo” but if you just want to cure the low speed “jerking” then the “Easy” unit does that.

Totally transformed the bike in traffic/city riding.
 
#24 ·
People, no amount of re-mapping is going to change the inherent character of these engines. they are HIGH PERFORMANCE singles. They rev to 10k rpm. The old british singles were not high performance and they had heavy flywheels to smooth them out, these motors are completely different. Trying to run them at 3000 rpm is a complete waste of time and lugging them at that speed can be damaging.

The only reason I can think of why people would want to do this is to get better fuel economy but that is not the way to do it. The best fuel economy is gained by running small throttle openings much closer to the torque peak of 7000 rpm.

Multi-cylinder engines will run smoothly at low rpm, a single will not.
 
#25 · (Edited)
Sorry but l have to disagree in part, primarily because my Duke 390 now runs fine at low RPM after fitting the box mentioned above.
Sure it’s not going to pull away from 1,000 rpm like my Z1000 did, but there’s no reason to have to slip the clutch in traffic at under 4,000 rpm.

I can accept that these bikes run rough at low RPM due to emissions limitations but it can be cured, without removing the CAT or modifying anything else on the bike.

Fuel consumption has remained about the same, its only a minor fuelling tweak at certain RPM.
 
#28 ·
The powertonic only changes closed loop. Open loop is controlled by afr reading from lambda sensor. That is where problem is. They made the bike lean to meet imission standards. Get a box that changes signal from lamba scensor or make your own if you have a way to measure the afr. Its basically just a resistor.
 
#31 ·
Did you tell your insurance you fitted it? My insurance would only list it as a "power commander" despite the fact that it doesn't increase the power of the engine at all, it only makes it smoother at low RPM

They basically wanted to increase the premium from £110 to £250

So l had to disconnect it and am back to slipping the clutch at low RPM.

Can someone recommend me an insurance company that knows the difference between a Power Commander and a Rapid Bike Easy !!

With cars there's companies who specialise in modified vehicles, the insurer for my modified Clio 182 didn't load the premium for the remap, Janspeed exhaust, lowered suspension, airbox, etc
As they knew what these things were.
 
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