Stihl MS500i chainsawStihl MS500i chainsaw

Fuel injection revolutionised automotive petrol engines in the 1980s and more than 30 years later, Stihl is hoping it will do the same for chainsaws.

The maker’s newly launched MS500i is apparently the first commercial chainsaw to do away with chokes and priming bulbs, with all fuel delivered to the cylinder via an electronically controlled injector.

As well as giving it higher torque than the best of the firm’s current models, it will offer faster acceleration too. For example, the latest top-end MS462 carburettor saw (see below) has a 0 to 100kph speed of 0.3s, while the 500i does it in 0.25s.

The injection system is also lighter, giving a higher power-to-weight ratio of 1.24kg per kW, and it has a lower gyroscopic force. This has been achieved by reducing the height and weight of the flywheel and means it should be easier to handle and control.

The company says the injection system will also react faster to changing conditions, such as the temperature, or oxygen content of the air. It should be easier to start, too.

Stihl hasn’t revealed too much detail about how the MS500i’s system works, but it’s likely to be the same, or very similar to the TS500i disc-cutter that’s already on the market.

See also: Video: Electric chainsaws on test

Injection system

This machine’s injection setup is made up of several components. Firstly, there’s a generator, which provides the power for the whole system and continually monitors the crankshaft position and engine speed. There’s also a temperature and pressure sensor in the crankcase.

Both of these feed their information into the injection controller, which does the clever bit. This constantly analyses the readings from the generator and sensor and works out how much fuel is needed, how long the injection interval should be and the appropriate injection timing.

It then sends this information to the injection valve, which sprays the desired quantity of fuel directly into the crankcase.

To make sure there’s always enough petrol available for the injector to work with, there’s also an injection pump that keeps the fuel line at a constant pressure.

Stihl MS500i chainsaw

Stihl MS500i chainsaw

Other changes for the 500i include a redesigned bumper spike and raised plunge bar that makes the saw easier to control when performing plunge cuts. There are also captive nuts on the chain sprocket cover to speed up chain changes.

Many of these upgrades have been rolled out to the maker’s other top-end saws, too.

The 500i will be available in limited quantities for the 2018/2019 season and will be getting its first public demo at the Arb show at Westonbirt Arboretum, Gloucestershire, on 11 and 12 May 2018. Prices are still to be confirmed.

MS462 CM

As well as its fuel injected saw, Stihl has also introduced a new 70cc machine in its professional-range of carburettor saws.

The MS462CM replaces the MS441 and MS461 machines and offers more power as well as lower weight. This means its 72.2cc two-stroke develops 6bhp and it weighs in at 6kg.

It comes fitted with the maker’s Mtronic engine management system, which automatically adjusts the carburettor to changing conditions. To do this, it takes readings such as temperature, altitude and fuel quality into account. After 72s of running it should have calibrated itself.

Even after a cold start it will remember the settings used last time it ran and, providing the conditions are the same, it will run correctly from the off.

Other features include a decompressor for easier starting, an improved anti-vibration system and a few features already mentioned on the MS500i.

The saw is available with an 18”, 20” or 25” cutterbar, which have list prices of £970, £985 and £1,000 respectively.