Chainsaw Won't Start after sitting

It was running fine when I put it away! As a small engine mechanic, I hear this complaint a ton.

So what’s wrong with a chainsaw that won’t start after sitting? The top five reasons your saw won’t start after sitting include:

  1. Bad gas
  2. Clogged carburettor
  3. Plug fault
  4. Flooded engine
  5. Faulty armature

On this page you’ll learn all about the most common reasons your saw won’t start, you’ll learn how to diagnose your problem quickly, and how to fix it. You’ll also learn my top tip to prevent this happening ever again, guaranteed!

Chainsaw gas with 2 stroke oil

Gas older than 1 month is stale

1 Bad gas

Gas gets over looked, a lot. We always assume there’s a major problem with the oily parts of our kit, when very often the problem is pretty easy to fix.

Gas goes stale, and you may be surprised to know that it can go off in as little as one month. It looses it’s Oomph, the symptoms include, no starts, lacks power bogging down, stalling, surging and everything between.

Lots of gas today is a blend of ethanol, this type fuel attracts moisture, and that invites trouble.

When a customer shows up in my workshop complaining of  a lazy starting saw after sitting, I’ll always suspect bad gas.

I have a pretty good nose for bad gas. If you suspect that your gas is older than one month, then go ahead and empty the gas tank the gas tank and fill with a fresh mix of gas and two stroke. For many saws this is enough to get the saw recommissioned.

Gas shot

If after refilling with fresh gas the saw still won’t start, I’ll try a gas shot directly into the carburettor. Because sometimes bad gas needs a little help to flush from the carburettor.

The results of the gas shot will have three possible outcomes.

Go ahead and try the gas shot,  remove your air filter (most saws won’t require any tools). Take a cap full (thimble size) of fresh gas and drop it into the carburettor.

Go ahead and try to start the saw in the normal way.

Outcome 1: Saw starts and stays running, you got lucky and your work is done sir.

Outcome 2: Saw runs and stalls. Repeat the process 2-3 times and if it continues to stall, you’ll need to remove and clean the carburettor (see clogged carburettor).

Outcome 3: Saw makes absolutely no attempt to start. You may have a ignition system fault (see plug fault)

Chainsaw carburettor

Clogged Carburettor

2 clogged carburettor

Unfortunately, we’re going to need to perform surgery on this patient. The stale gas has likely congealed inside the carburettor and blocked up tiny fuel passage ways. It’s not uncommon to remove the carburettor and find it’s too badly clogged to repair.

Carburettor manufacturers offer carb kits that include gaskets, gas needle valve and arm. It’s good practice to replace these as your going to dismantle the carburettor anyway, but it is possible to reuse the same parts.

As an alternative just go ahead and replace the complete carburettor as you’ll find in most cases replacement carburettors aren’t expensive. New carbs come with a guarantee, tested, tuned and ready to fire out of the box.

If I have any doubts about the carb I’m working on, I’ll bounce for a new one.

tools you'll need

Removing the carburettor on some chainsaws is a pain in the ass, but for most you’ll find it straight forward.

But working on saws isn’t like working on your car, truck or even mower. The parts are tiny and real-estate tight, You’ll need bags of patience and if you’ve got Shrek hands, you might want take a pass on this repair.

Special carburettor adjuster tools will be needed for some saws, but other than that just a selection of sockets, screwdrivers, carb cleaner, carb cleaning tools and my special top tip – gas stabiliser additive to stop this from ever happening again.

You can check them all out here “Chainsaw parts & tools”

Replacement carburettors

If you’ve decided to replace your carburettor, be sure to order the correct model.

Your carburettor is calibrated to the power out put of your saw. So, although a family of carburettors look identical, they are different.

You’ll find most saw manufacturers don’t actually make their own carburettors. They use third party well known and trusted carburettor manufacturers, like Walbro and Zama.

So when you have removed your carburettor check the make and model stamped into the body of the carburettor. Then check out this page “Small engine carburettors”, I’ve listed all the most common types where you can check price and availability on Amazon. “Chainsaw parts & tools”

After cleaning or fitting a new carburettor, be sure to clean your gas tank and fit a new gas filter.

Chainsaw plug

Check Plug

3 plug fault

Plugs have tough job, and they live in a hostile environment. They’re right there in thick of all the action. Wedged in a hot cylinder next to a hot muffler, it’s no wonder they are number three on the list of possible causes. You’ll find plugs are pretty tough components, they can work tirelessly for years without ever missing a beat.

A plug should be changed at the start of each new season, but I live in the real world and most owners won’t give the plug a second thought, so long as it s doing its job.

If you are treating your saw to a new plug, be sure to get the right one, plugs come in different thread thicknesses, lengths and heat ranges.

Check your make and model for the correct spark plug part number.

Checking Spark

A spark plug test tool is the best way to check the ignition system. The tool stresses the ignition system and if it’s faulty it will show up. Don’t have a spark test tool? Not to worry, we have a hack.

Checking spark without a test tool, go ahead and:

  • Remove the spark plug
  • Ground the plug body against the saw metal body (I use a jump leads to help get a good connection)
  • Set the switch to “On” and pull start the saw
  • Observe the spark plug for spark

If you’ve got spark, great! All is good here.

No spark from plug

No spark at the plug doesn’t necessarily mean you have a major problem.

Check your plug, there should be a a visible gap between the tip and the electrode. If the gap is closed, open it using a pliers or flat screwdriver.

The plug should be free from oil and carbon, if not clean the plug using a wire brush. Now test again for spark.

Or if you have a spare plug or a known good donor test plug, swap it. Now crank over the engine and check for spark again. Still no spark, you’ll need to check the armature (See below).

Chainsaw flooded with gas

Flooded

4 flooded engine

So what is flooding? It’s basically too much gas in the combustion chamber, of the engine. Instead of the spark plug igniting the gas, the excess gas simply extinguishes the spark. No spark equals no fun!

So why does it happen? Flooding often happens when the engine is repeatedly cranked over without the engine actually starting. It very often occurs as a result of another underlying problem, such as bad gas, bad spark plug, overuse of choke or just a faulty carburettor.

A saw that isn’t well maintained is prone to flooding.

So how can you fix it? There is three ways to fix a flooded chainsaw:

  1. Just let the saw sit for 30 min and the excess gas will evaporate.
  2. Remove the spark plug, dry it, crank over the engine a few times to dry the cylinder. Now refit the plug and try again.
  3. Set the switch to “On”, set throttle to fully open, set choke to “Off” and crank over the engine. Expect the saw to start on the second or 3rd pull.

How can you prevent flooding? Make sure your gas is fresh and your saw is tuned-up.

5 faulty armature

A faulty armature (aka a coil) is a pretty common failure. The armature with the flywheel creates the high voltage the spark plug needs to fire.

Armatures commonly fail in one of two ways. They will often work OK when the machine is cold and then stop working as the machine heats up. Or, they’ll just stop working period.

Testing the armature

Testing the armature starts with the spark plug test we did earlier, ideally we would use a proper tool to test the ignition system. The test tool loads up the armature and will reveal any weakness, our hack with the plug isn’t fool proof.

You can check out the test tool on this page along with some other useful kit “small engine repair tools”.

Testing is simple, go ahead and:

  • Remove pull assembly cover (4 screws usually)
  • Remove coil control ground wire
  • Refit pull assembly
  • Check spark as before

Still no spark? go ahead and replace the armature.

Or if you now have spark, check for shorting on the on/off switch wiring (damaged wiring).

Damaged coil wire

Damaged Wire

Damaged plug wire seen here in centre of pic. This is a common issue as chain saws cause lots of vibration.

Related Questions

How do you fix a seized chainsaw? A seized chainsaw will require a new cylinder head, piston and possibly a new crankshaft and con-rod. Fixing a seized chainsaw usually isn’t economically viable.

Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.