Your modern chainsaw has a precision engine that can be rendered into a worthless chunk of aluminum with just a few careless mistakes, like running straight gas through it, or spending an afternoon trying to force the saw to cut with a dull chain. You can also damage your saw by not properly maintaining the engine’s components.
Most chainsaws have two-stroke engines that require lubricants to be added to the fuel; two-stroke engines aren’t lubricated through a crankcase, like a four-stroke vehicle engine is. Each saw has a specific ratio of fuel to oil that is required for optimum engine lubrication and it’s very important to get this mix right. My saw runs on a 50:1 mix.
It’s important to add the right lubricant, as two-stroke oils for air-cooled and water-cooled engines are formulated differently. Forget about using TC-W3 oil, as it’s designed for water cooled engines that run at low RPMs. It will work in a pinch in chainsaws, but long term it’s not good for them. If you’re buying from a store that doesn’t specialize in chainsaws, be sure to read the fine print on any bottle you buy.
Once you’ve got the right oil, it’s important to mix the fuel properly. And don’t forget to shake the container before adding fuel to the saw, as the mix can separate during storage.
Properly mixing your fuel will go a long way to preventing engine fouling, but regular engine maintenance is also important. To access your saw’s engine, remove the engine cover by loosening the screws or clips that hold it in place. You’ll see the spark plug, the air filter, some of the carburetor components, and the cooling fins at the top of the cylinder. Down by the pull cord you’ll see the fan that provides fresh air to the carburetor and cooling air to the fins.
Your saw breathes – it needs to be able to draw fresh air in, mix it with fuel, burn it, and then “exhale” it as exhaust. To run at peak performance, your saw needs to be able to do this with ease. Check your air filter after every eight hours of use. A dirty air filter can cause all sorts of problems, such as loss of engine power, excessive fuel consumption, and excessive wear to engine parts. Brush the air filter gently with a soft brush or wash it in warm soapy water then dry it. Do not use compressed air to clean it – compressed air can blow holes in the filter, allowing dust and debris into your carburetor.
On the exhaust side, check the spark arrestor periodically. It is a little screen that covers the muffler and can be removed by loosening a small screw. I once saw a saw with an arrestor so plugged with carbon that the starter cord could barely be pulled – the saw couldn’t exhale!
If your saw is difficult to start, low on power, or idles poorly, it might be the spark plug. Remove the plug and check it; if it is dirty, you may be running improperly mixed fuel, you may have a dirty air filter, or you may have a carburetor that needs adjustment. Clean the plug and check the electrode gap – regap if necessary. If your air filter is clean and you know your fuel is good, have a qualified technician who owns a tachometer check your carburetor – trying to adjust those three screws yourself is another good way to end up with a useless chunk of aluminum. Chainsaw engines are air cooled by a flywheel fan that blows over several cooling fins, sort of like a crude radiator, and overheating can ruin your saw. The fins present a larger surface area for the fan to cool, but if the spaces in between the fins are clogged up with oily sawdust or gunk, they can’t efficiently cool the engine. Take the cylinder cover off the saw periodically and clean between the fins with a soft paintbrush or toothbrush.
If you bring the same good care and focus to engine maintenance that you use in making sure your chain is sharp, your saw’s engine should last you many seasons of work.