Electronic fuel injection

Traditional chainsaws are fitted with carburetors to meter airflow and fuel mix so that the engine will operate optimally. The Stihl MS 500i is the first standard chainsaw to be electronically fuel-injected.

The electronics become visible when the top cover of the saw is removed. The absence of a carburetor also means no manual settings are needed as the saw has fully automatic engine tuning.

Stihl's MS 500i is the first electronic fuel injected saw on the market.

Electronic injection has five main parts:

  • Generator: producing all the power for the controller and relaying engine speed back to the controller.
  • Sensor: measuring both speed and pressure within the crankcase, transmitting data back to the controller.
  • Controller: constantly analysing generator and sensor data to control fuel injection and ignition accordingly. Air mass is determined from temperature and pressure data within the crank case.

    This information is used with speed data to work out the quantity of fuel needed, injection duration and appropriate injection timing.

  • Injection pump: keeps fuel pressure constant.
  • Injection valve: when triggered to do so, it sprays the optimum quantity of fuel directly into the crankcase.

    • The MS 500i we tested is a professional saw. Saws generally come in three categories – hobby, semi-professional and professional.

    Its electronic components are accessible once the cover above the grip is removed.

    So from the beginning, I had high expectations for the MS 500i as I am more used to the typical semi-professional farm saw.

    The saw was tested on large seasoned ash and oak trees that had fallen some time ago, giving a mix of both light and heavy cutting.

    The saw was fitted with a 20in bar and 3/8 pitch chain, although more than capable of holding a larger bar.

    Operation

    Upon lifting the saw, I immediately noticed the absence of switch indicating if it was in on, off or if the choke was engaged. Instead, the MS 500i has a stop button and a priming bulb.

    The stop button and priming bulb is simple and effective.

    After stopping and starting the saw a number of times, I liked the way in which I didn’t have to ensure the saw was in the on position and engage the choke before pulling the cord (when cold).

    I could just press the primer four or five times on a cold start then pull the cord and straightaway the saw would roar into life.

    Similarly, when stopping the saw I could just hit the stop button and the saw would die out.

    The saw also has a decompression valve to ease starting, but this new injection system seemed to allow the saw to start up quite easily anyway.

    The saw features a decompression valve almost standard on the majority of Stihl saws at this stage.

    Both fuel and oil tank caps are conveniently opened and closed by hand using the easily gripped flip-up catches.

    Access to the air filter is easy. Simply twist the black knob above the hand grip and you’re in.

    Reaching the spark plug requires a flat-headed screwdriver or chainsaw combination tool to loosen the one screw holding the cover in place.

    The air filter is easy accessed and easy removed requiring no tools.

    Captive nuts holding the bar in place eliminate the risk of losing a nut. The saw features Stihl’s anti-vibration system which claims to reduce vibration present in its handles, which I found worked as vibration was minimal for a saw of its size.

    Tensioning of the chain is simple. Just loosen the captive nuts slightly and adjust the screw between the nuts with the combination tool, then tighten the captive nuts again.

    Just as you would expect from a professional chainsaw, all maintenance points are easily accessed and the saw is well-built, feeling well-balanced in hand.

    The MS 500i boasts impressive specs, claiming to have the best power-to-weight ratio on the market, weighing in at 6.2kg and outputting 79.2cc (5kW), creating more than 6.8hp.

    This gives it a power-to-weight ratio of 1.24kg/kW and perhaps makes it the first chainsaw to have a higher horsepower than weight in kilos.

    Having used the saw over the course of the day, I was impressed with its power-to-weight ratio, being used to a semi-professional MS 391 outputting 64.1cc and weighing in at 6.4kg.

    The saw proved more responsive than any saw I have used before. As soon as the trigger was pulled, the saw was reaching full speed. Data sheets claim the saw has abilities to accelerate to 100km/h in as little as 0.25 seconds, which I would well believe.

    Verdict

    The raw output of this new saw, combined with its power-to-weight ratio, puts the MS500i in a class of its own, leaving me looking forward to hopefully seeing fuel injection technology integrated in semi-professional farmer-spec saws in the future.

    Everything from the saw’s appearance, usability and its torque was impressive, never missing a beat throughout the day.

    It seemed a little hard on fuel, although I did spend most of the day putting the saw through its paces cutting large-diameter trees.

    In theory, electronic fuel injection should allow the saw to run on less fuel than a conventional saw.

    Having said this, it is important to take into account the whopping 6.8hp it produces, which would require more energy than most of the saws we have tested, so at this point it is hard to make a statement on fuel consumption along with fact the saw was new when we tested it.

    The price of €1,800 including VAT leaves it hard justified for the average farmer clearing the occasional fallen tree and removing branches in fields or across laneways.

    But for the serious user requiring daily use of a saw, I would highly recommend the MS 500i as it boasts unmatched specifications, such as its unrivalled power-to-weight ratio.

    Specifications

    Engine size: 79.2cc (5kW).

    Bar length: 20in.

    Weight: 6.2kg.

    Fuel tank volume: 0.78l.

    Oil tank volume: 0.325l.

    Power to weight ratio: 1.2kg/kW.

    Sound power level: 119 dB(A).

    Sound pressure level: 106 dB(A).

    Price: €1,800 including vat.