Engine Tuning 101

There are several basic tasks that must be carried out to achieve decent engine performance, which this guide details: fuel and ignition map selection, throttle position sensor (TPS) calibration, throttle body (TB) synchronization, throttle cable tension adjustment, idle adjustment, and ensuring there are no leaks (air or exhaust). A full tune, including all of the above, should be performed when derestricting.

With a bad tune these bikes may in any combination hard-start, backfire, surge, sputter, you name it, regardless of being restricted or derestricted. I rode my SXV 550 a week restricted with no problems whatsoever; it started and ran fine. When I had it derestricted, the first dealer loaded the wrong map, the second dealer calibrated the TPS incorrectly, and the third dealer did a half decent job, but the bike still backfired a lot. Finally, I said screw it and decided to do it myself. About two hours later it started on the first try and ran like a dream. What a difference!

A Word About Derestriction

These bikes are meant to be run derestricted; it's simply what the designers and engineers had in mind. I regret my bike has a fair amount of blow-by now, which I attribute to not breaking the engine in hard during the first week while it was still restricted. That said, derestricted, the bike is a whole different kind of awesome. Highly recommended! —altaic


  • TuneBoy ECU interface
  • CarbTune (or similar) multi-port vacuum gauge
  • A long philips-head screwdriver


Ensure There Are No Leaks

First things first: replace the front and rear exhaust gaskets. Also, check to make sure the throttle bodies are securely tightened to the engine. This is important, because a small leak will affect the fuel/air mixture in the engine, rendering the tune bad.

Choosing and Uploading Fuel & Ignition Maps

Choosing the correct tune basically comes down to what bike you have and the silencer installed. Restricted bikes basically just have baffles in the standard silencer creating a restriction (they also have a throttle stop that limits how far the throttle opens). Have a look at the ecu software matrix, and you should be able to spot your bike (the newer maps have higher numbers). For instance, my SXV 550 with a derestricted standard silencer uses the new (at the time of writing this article) 15017 map.

Note About Custom Or Non-Aprilia Aftermarket Silencers

These fall in the realm of custom maps, which is outside of the scope of this guide. While TuneBoy does let you edit the maps, expensive equipment (dyno, gas analyser, etc.) and experienced guys to operate it are almost certainly required to turn something useful out. I'm happy to host custom maps or start a map/silencer cross-reference section (for manufacturers who designed their exhaust to be used with the available maps), though. Please contact me on ApriliaForum if you'd like me to host your maps or info. —altaic

To upload the map to the bike's ECU, we'll be using TuneBoy:

  • Ensure the latest TuneEdit software updates are installed.
  • Download the TuneEdit tune that corresponds to the map you chose, and place it in TuneEdit's tune directory.
  • Plug the TuneBoy USB cable into the computer, which should be situated near the bike.
  • Hook the cable up to the ECU interface on the bike, and clip the ground wire to a bolt on the engine or something.
  • Open TuneEdit. It will ask you to select a tune if you haven't already, so select the tune you downloaded.
  • Turn the bike on (don't start it).
  • If you haven't done so yet, register TuneEdit. Go to the menu Tools -> Get ECU Serial Number, and email the information to AF1 (if you got it there). They'll send you a key that you have to enter in the menu Options -> Properties, which will enable TuneBoy for your bike.
  • At this point the values at the bottom of the main window should now display information rather than all zeros, and the Download button on the lower right should glow orange. If not, you may have to restart the program with the bike powered off and then after the program reopens, turn the bike back on.
  • Click the Download button and follow the prompts.

Calibrating the Throttle Position Sensor (TPS)

Again, we will be using TuneBoy to interface with the ECU:

  • Picking up from the previous section, TuneEdit should still have a connection to the bike's ECU.
  • Select the menu Edit -> Tune Constants, and twist the throttle on the bike to verify that the TPS value changes.
  • Unhook the throttle cables from the throttle grip, in case they interfere with idle (properly tensioned cables should not).
  • Unscrew the idle adjustment screw on the left side of the airbox, taking care to not letting it drop out if you can. You can watch the TPS value slowly lower as you do this, and it will stop when the idle screw is about to fall out. If the idle screw falls out as it did with me my first time, you'll have to remove the airbox top and sides (5 screws) with the long philips-head screwdriver, and fish the idle screw back in place (kind of a pain in the ass).
  • Click the "Set low" button right below the TPS value display (the value was 39 on my bike).
  • Hook the throttle cables back up to the throttle grip.
  • While holding the throttle wide open, click the "Set high" button (the value was 214 on my bike).
  • Close the Tune Constants window.

Setting Idle Level

  • Picking up from the previous section, we'll be using the "Current TP" display at the bottom of the main TuneEdit window. It shows relative throttle position, that is, a percentage between the min and max TPS values you set before.
  • Unhook the throttle cables from the throttle grip.
  • Screw the idle adjustment screw in until the TPS value displayed is 3.0, which will be in the ballpark and allow the bike to start and idle.
  • Start the bike and adjust idle to about 2000 RPM when the bike's warm.
  • Hook the throttle cables back up to the throttle grip.

Adjusting the Throttle Cable Tension

Setting the throttle cable tension properly is important for the functionality of the yellow fast-idle button. The pull cable pulls the throttle open when you twist the throttle grip, and the push cable tensions the throttle grip. There should be a little play in the grip, roughly 2mm. If the push cable is over-tensioned, the yellow button will make the fast-idle too high. If the push cable is too slack the yellow button won't do anything. I managed to fiddle with both cables until I got it right; I have to go back verify that this information is all correct.

Synchronizing the Throttle Bodies (TBs)

Disclaimer: This is a tricky procedure that may take a while to get just right. You may want to use a fine marker to mark the throttle synchronization adjustment slot before starting.

  • Remove seat and lift tank.
  • Disconnect the hoses connected to the right side of the airbox. These are the atmospheric pressure pickup and the oil breather hose.
  • Remove airbox top and sides (5 screws) using your long philips-head screwdriver, being careful to not lose the airbox screws.
  • Remove the rear cylinder end of the vacuum hose that links the vacuum ports of the two TBs together. This is called the bypass hose.
  • Connect a hose identical to the bypass hose to the rear cylinder vacuum port, so you now have two identical hoses hooked up to the front and rear TBs. It is important that the hoses be identical, because they may otherwise sustain vacuum differently.
  • Connect those hoses to two of the CarbTune hoses using adapters (IIRC, the CarbTune comes with the adapters).
  • Fire the bike up and compare the levels of the two TBs on the CarbTune.
  • If the levels on the CarbTune are different, loosen the TB synchronization adjustment screw (TBSS) just enough to be able to move the rear butterfly valve arm a little with a light tap of the screwdriver.
  • Make fine adjustments using light taps, preferably with the CarbTune hanging in front of you to make sure you're causing the two levels to converge on being equal.
  • Once they are equal, tighten the TBSS, taking care to not allow the torque of the screw to shift the synchronization.

Now the TBs are synchronized at idle. You think, "Great! We're done… Right?" Nope! The two cylinders actually have slightly different vacuums at different RPMs, which means that synchronized at idle doesn't mean it's synchronized at the RPMs that probably matter more to you. Blip the throttle and watch the vacuum levels drift.

So, now you'll probably want to repeat the last three steps while blipping the throttle (tighten the TBSS before blipping the throttle!), making minor adjustments away from idle sync, towards your mid/high RPM sync. The problem is, you don't want to make idle unstable and also make the bike hard to start. So, I usually adjust towards the higher RPM sync until idle becomes a bit unstable, and then adjust back a titch. Once you're satisfied, put her back together. You're done!


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