100 MPG Madness, Project Aprilia SR50 Part 5- More Power!


 Project Aprilia SR50 more power!
The intake, throttle body and air filter really clean up the cluttered side of the bike and sure look race oriented!

While thinking about what to do next, we installed one of High Gain Tuning’s advance keys.  This is a flywheel key that advances the ignition and injection timing 3 degrees which makes for a more stable idle and gives a boost in power. We noticed better acceleration but no change in top speed with the key in place.  Our scoot still delivered 110 mpg plus as well.

 Project Aprilia SR50 more power!
High Gain Tuning’s fuel pressure regulator set is very high quality and complete.  We opted for the optional braided steel lines and AN fittings.

Since we had determined that our scooter needed more fuel to take advantage of our improved breathing to make more power, we were at a loss of how to get it.  We could not get the code to hack into the ECU.  However High Gain Tuning came to our rescue with their adjustable fuel pressure regulator.  The High Gain system overrides the factory pressure regulator and allows you to increase the fuel pressure to the air assisted injector to richen the fuel mixture.

 Project Aprilia SR50 more power!
Although not super complicated, the installation of the regulator requires the disassembly of quite a bit of the scooter.  It’s not for the mechanically lame!

In stock trim the SR50 runs about 100 psi of fuel pressure at idle.  By experimenting we found that the bike ran best at over 120 psi which is close to the dead head pressure of the fuel pump!  However there was an idle stability and stalling issue at pressure this high so we turned the fuel pressure back down to 118 psi or so.  The idle isn’t perfect but we will take the power increase any day. The difference was amazing; the bike woke up, as we theorized the diesel like DiTech needed more fuel to make power.  Top speed was now 65 mph!  Not bad for a small engine class scooter.

 Project Aprilia SR50 more power!
 The regulator takes its high pressure reference from the top of the air injector.



  1. Bonjour
    Pouvez vous me donner le branchement des durites du régulateur de pression essence et l’affectation de chaque durites s’il vous plait je suis en france et j’ai pas ce type de pieces toutes faites
    Can you please give me the connection of the fuel pressure regulator and the assignment of each hoses
    Thank you , l’m in France

    1. The regulator goes inline between the fuel pump and the injector. You need to take the higher pressure reference for the regulator off of the top of the air injector.

  2. Hello, I also want to install the larger throttle valve (26mm) on my Gilera Runner Purejet. However, I can’t find these anymore. Are these still available to buy somewhere or do you still have one? Kind regards from Germany Victor

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