KTM Duke II - Open airbox and jet kit

Like most stock bikes Duke II has a very lean carb setup. Knowing this, fitting a carb kit to richen up and optimize the mixture is almost as logic as filling gas. Reaching high revs you'll notice the power fades away.

The carb kit (leistungssteigerungs-paket in German) is provided by Sommer, Schneider or other dealers, and consists off the following parts:
  • Stainless steel open airbox-lid
  • 165 or 170 (competition) main jet
  • 1.1 Pilot air jet


In the sommer brochure they explain how it has to be installed, but it's in German, so I'll tell it how it worked for me.

This is the easiest part... no explanation needed, just swap it! Or... as you'll read later, leave it off!

Main jet
The main jet is located at the bottom of the float bowl. Just remove the central bolt in the middle. The main jet is right behind it and can be changed through the hole. Don't forget to let the gasoline out first!

The pilot-air jet is located in the intake of the carburettor. To reach this you have to remove the rubber between the carb and the airbox.

Idle mixture adjustment

According to the Sommer-catalogue the standard setting of the idle mixture screw is 3,5 turn out from closed and should be set leaner after the installation of the jets. My standard setting turned out to be only 2 turns out... so I had to do the quick and dirty method:

Warm up your bike ( at least a 10-15km ride)
While the engine idles, slowly turn the idle mixture screw in (leaner) until the engine starts to run bad.
Then start turning it out (richer) until the engine starts to run bad again and count the turns.
The right setting is in the middle of these to positions.
For hot conditions (e.g. summer) and/or mountains you might set it a quarter turn leaner (in).

The best way is to use a gas-analyzer and measure in the header pipes (not at the end in the silencer).
For that purpose we modified our header pipes.

Mikuni CV Carb
Here we have a drawing (click to enlarge) of the Mikuni CV carb with all the necessary details
  •  Mikuni CV Carb
    (1) Pilot-air jet
    (3) Main Jet
    (9) Idle mixture screw

The bike accelerates much better and reaches high revs much easier. Max power is approx. 55.5bhp, max torque approx. 64Nm. We still have to measure the standard values. Also we have to determine if the air box-lid can stay removed. The graphs looked -slightly- better without the lid (graphs will follow).

Fuel consumption is still good, almost 18km on 1 liter during fooling around and having fun.

There is also more intake-noise. It's a low thumping noise.

Good value for money, even better when you don't buy the open air box-lid.

Last modified: 07-09-2009