Tuning: More fuel necessary?

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    -Acra slip-on

    -K&N airfilter in a modified airbox


    Can the original ECU adapt to this changes or is a aftermarket solution necessary?

    Since its only a 400cc bike its not worth 500usd+shipping for example Coober ecu.

    Its winter here in Sweden so I cant test it and check sparkplugs etc

    If needed, has anyone done a proper test of Boosterplug?




    Only proper way to find out is stick it on a dyno and measure the afr.

    Personally I think people overestimate the ‘tuning’ capacity of the stock ecu.
    As far as I know the ecu on modern bikes only adjusts the fuelling using the lambda readings on small throttle openings at low revs.
    And why is a 400cc bike not worth a decent ecu? You obviously thought it was worth the decat, akrapovic and K&N filter? They add up to quite a few euros as well. Why invest in those and not finish it properly with some dynoruns and mapping it properly?

    • This reply was modified 1 year, 11 months ago by Nampus.



    Well, Acra came with the bike and decat I did myself.

    Is there an alternative to Boosterplug for the 401? Theres several for 701.

    I see that many here drill holes in the airbox-lid. That is the wrong way to do it.

    Will send unfiltered air to your engine since intake is above the filter.


    @Dennis  I read on the duke 390 forums about guys drilling their airbox covers and installing these little filters in the holes (Link below). This solves the concern of letting in unfiltered air. Also I have not yet installed the booster plug, but I have watched a few reviews and all seem to be good. I also can’t justify spending the money for the Coober ECU, when a slip-on, de-cat, added airflow, and booster can equal less than $500 total.




    Whilst I have the 701, have installed the boosterplug and the airbox mod with three holes and added foam underneath the holes.

    Been very happy with the results, the boosterplug definitely smoothed out the acceleration and I feel it has a bit more at that low to medium rev range.


    I tried the boosterplug and the rapidBike easy together which richened things up in open and closed loop but now i’ve gone back to just the RBE as I mainly wanted to reduce the sudden transition from lean to rich when you open the throttle, along with the loss of torque when settling at cruising revs.

    Cheap option is just unplug the 02 if you can deal with engine light, made things a lot smoother for me.

    Powertronic is cheap but the one I got wouldn’t read the throttle position. Planning to try the full race rapidbike for the later throttle-by-wire duke, mainly for the engine brake reduction feature.

    This is with a stock bike though.



    can you really unplug the O2 sensor and get the engine to run richer/smoother?

    i’d like to test this, if knowing somebody else tried this too on the 401.



    I too would like some solid input. My new 18 vit 401 – just installed de-cat. Can i run stock ecu safely? Seems to run good. If no is there a budget way to richen up afm? Thanks.


    Forget about  Piggyback ECU, remap, and all that crap…

    Subtitute the stock 3.0 BAR FPR and install at you fuel pump a 3.5 BAR fuel pressure regulator. Let the stock ECU do the adjustment in closed loop via stock lambda readings.

    In open loop the new  FPR will provide enough fuel to avoid lean conditions and to make power with exhaust and air box lid upgrades.

    Use iridium spark plug.

    Cheap and effective.


    Athal that is very/interesting and helpful guidance! Have yet to hear about this solution and like it! Thank you! Curious of 2 things:

    1. Have you or anyone u have seen done any air/fuel testing with proposed setup or just going on feel/exhaust sound?

    2. Do u happen to know manufacturer/part number to 3.5 bar fpr and part number to applicable iridium plug?

    Thank you so very much for chiming in! Sounds invaluable.


    Here you get it:

    Fuel Pressure Regulator: 3.5 Bar 42€

    There’s also a 3.2 BAR option and 4.0 BAR option…

    You only need to install and run test. Use an OBD cable, a bluetooth OBD dongle and you android phone to read lambda O2 sensor while you drive full throttle to burn gasoline… Or you can Dyno run and wide band lambda test to burn money.

    This engine has high compression ratio, 12,5:1 and factory set up is to run on the lean side (Euro4), so to avoid knocking I always use the higher octane available fuel.

    Heat wrap your 2018 bike’s exhaust. Is routed near the air intake an TBI and hot air also can cause engine knoking…




    Sweet Athal ty for sharing w us all!!


    Complete recipe awaiting to content moderator  supervision…


    Good job Athal!

    Pretty sweet hack.

    Thanks again!

    Adam in Dallas



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