Variable pulse length or changing pwm frequency for injection

Hey guys,

I posted earlier on the Dutch part of the forums, but no one has replied for a while, so..

I am doing a school project with a friend of mine. We are trying to build a injection system (http://en.wikipedia.org/wiki/Fuel_injection) on a Puch Maxi 50 cc two stroke moped. I'll spare you the mechanic details.

We thought that the Arduino would be a good choice to control the injector. I'll explain the problem. The moment where the injector should inject the fuel is determined by a photo sensor like this: http://www.conrad.nl/ce/nl/product/179999/Vertakkende-lichtsluis-EE-SX1041-Omron-EE-SX1041-Vork-lichtslot-Bereik-5-mm;jsessionid=327EDC5549B43C81F0DFF2FEA9F8B53D.ASTPCEN20?ref=list. The arduino must send a pulse of pre-determined length to the injector. This must happen when the sensor gives a HIGH signal. Is it even possible to send a pulse like this, and if yes, what command or what commands should work?

If something seems vague, please don't hesitate to ask.

Edit: Forgot to mention, this could also probably be solved by adjusting the PWM frequency, if that is possible.

Edit2: Solved the problem already. Can be closed.