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:
- Bad gas
- Clogged carburetor
- Plug fault
- Flooded engine
- 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!
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. If your saw is new and won’t start, stale gas is likely your issue. 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. I advise all my customers to use gas stabilizer in all their small engine kit. It prevents the gas going stale and prevents hard starting and gumming of the fuel system a common occurrence in kit that spends a ton of time sitting idle.
NOTE: Gas stabilizer is not a substitute for 2 stroke oil, you must continue to add the 2 stroke as before. You’ll find a link to the stabilizer I use here on the “Chainsaw repair tools” page.
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 and fill with a fresh mix of gas and two stroke. For many saws this is enough to get the saw recommissioned.
If this doesn’t work for you, then try the gas shot, and that’s what we’ll cover next.
If after refilling with fresh gas the saw still won’t start, I’ll try a gas shot directly into the carburetor. Because sometimes bad gas needs a little help to flush from the carburetor. Go ahead and try the gas shot.
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 carburetor intake.
Go ahead and try to start the saw in the normal way.
Three outcomes are likely:
1 – Saw starts and stays running, you got lucky and your work is done!
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 carburetor (see clogged carburetor below).
3 – Saw makes absolutely no attempt to start. You may have a ignition system fault (see plug fault below).
2 Clogged Carburetor
Unfortunately, we’re going to need to perform surgery on this patient. The stale gas has likely congealed inside the carburetor and blocked up tiny fuel passage ways. It’s not uncommon to remove the carburetor and find it’s too badly clogged to repair. Carburetor 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 carburetor anyway, but it is possible to reuse the same parts.
As an alternative just go ahead and replace the complete carburetor as you’ll find in most cases replacement carburetors 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.
Removing the carburetor on some chainsaws is a pain in the ass, but for most you’ll find it straight forward. Working on saws isn’t like working on your truck, car 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.
Tools You’ll Need – Special carburetor 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 stabilizer additive to stop this from ever happening again.
You can check them all out here “Chainsaw repair tools”.
If you’ve decided to replace your carburetor, be sure to order the correct type. Your carburetor is calibrated to the power out put of your saw. So, although a family of carburetors look identical, they are different. You’ll find most saw manufacturers don’t actually make their own carburetors. They use third party well known and trusted carburetor manufacturers, like Walbro and Zama.
New carb not expensive
So when you have removed your carburetor, check the make and model stamped into the body of the carburetor. Then check out this page “Chainsaw parts & tools”, I’ve listed all the most common types.
After cleaning or fitting a new carburetor, be sure to clean your gas tank and fit a new gas filter (inside gas tank).
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.
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 and reattach the plug wire
- Ground the plug body against the saws metal cylinder head (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
Ground spark plug
Two outcomes are possible:
- You’ve got spark, great! All is good here.
- No spark. No spark at the plug doesn’t necessarily mean you have a major problem.
Check your plug, there should be a visible gap between the tip and the electrode. If the gap is closed, it will need to be gapped or swap out the plug for a new on. Check out the “Spark plug gapping video” here. It’s for a lawn mower but the process is identical.
The plug should be free from oil and carbon, if not clean the plug using a wire brush. Check out the “Spark plug cleaning video” here.
Test Spark Again – 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).
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 carburetor. 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:
- Just let the saw sit for 30 min and the excess gas will evaporate.
- Remove the spark plug, dry it, crank over the engine a few times to dry the cylinder. Now refit the plug and try again.
- 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 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 “Chainsaw repair tools”.
Testing The Armature
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
Two outcomes are possible:
- Still no spark? Go ahead and replace the armature.
- You now have spark, check for shorting on the on/off switch wiring (damaged wiring).
Damaged Wire – Damaged plug wire seen here in center of pic. This is a somewhat common issue, saws create lots of vibration.
You may also find the “Chainsaw trouble-shooting” section helpful.
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.
Should I rev a cold chainsaw? It is advisable to allow a chainsaw warm up before running at full throttle.