You bought a new chainsaw, so you wouldn’t have to deal with this crap, right? I know it’s disappointing, but we’ll get it figured out.
So what’s wrong with a chainsaw that won’t start? The top seven reasons a new chainsaw won’t start.
- Air-locked fuel system
- Choke not on
- Primer bulb not pressed
- Flooded engine
- Incorrect gas mix
- Bad gas
- Plug wire disconnected
By the end of this page, you’ll know why your saw won’t start, and you’ll know how to fix it for free today. If your chainsaw was sitting for a long period with gas in the tank, check out this post “Chainsaw won’t start after sitting.”
This stuff is all pretty basic; you won’t need a degree in engineering to apply this knowledge.
Chainsaw Starting Procedure
My father was a mechanic, too, and when troubleshooting, he taught me first to verify the reported problem; I’ll confess I haven’t listened to all his advice, but this one is gold. This probably isn’t your first chainsaw, but it is a new saw, and so it may have a slightly different starting procedure to previous models you’re familiar with.
All chainsaws will have an on/off switch, choke control, and throttle lever, and some may have a primer bulb and a decompression valve. You’ll need to check your starting instructions user manual carefully.
A normal starting procedure goes like this:
- Check gas tank for fuel level and mix to the correct ratio
- Set switch to “On”
- Set choke lever to “Full”
- Press primer bulb 3-4 times (if fitted)
- Press decompression valve (if fitted)
- Pull the starter cord sharply
If the starter isn’t pulled sharply and with some force, the saw won’t start. Most saws likely won’t start on the first attempt but should on the second or third.
If you try more than 5 to 6 pulls, the cylinder will likely flood with gas. A strong smell of gas is one sign the saw is flooded; just allow the saw to rest for 30 minutes and try starting it again. A warm chainsaw may not need a choke to start, but a cold saw won’t start without a choke.
When I’m troubleshooting, I’ll do a quick visual of the saw and quickly rule out some of the easy-to-check stuff, some aren’t very likely to be the cause, but as they’re not difficult or time-consuming, I’ll check them anyway.
Here’s the checklist:
- Plug wire on and secure (I know for some saws this won’t apply as plug wires are pretty snugly fitted.)
- Next, I’ll check the air filter; I know the saw is new, and so the filter is new, so I’ll just want to see that the filter is in place and nothing is blocking the airway. Removing all modern saw air filters won’t require any tools.
- Lastly, I’ll check the gas. In the majority of cases, the fueling system is the cause of small engine no starts.
Your saw is new, so we know the carburetor is clean, right? But what if the gas you used was old or contaminated? Is that possible?
Gas from last season is stale; regular gas older than one month is stale and can cause all sorts of problems, no starts, poor running, lack of power, stalling, bogging down, etc. if you suspect stale gas, just empty out the tank and fill it with fresh mixed gas. The good gas will pass through the system, pushing the old gas out.
OK, that’s all the easy stuff checked.
Two-stroke oil mixed to ratio.
Your Saw Needs 3 Things
Now we’ll get down to the business end of diagnosing your fault. Small engines are very simple; they need three things to start.
Thing One – Your saw needs fresh gas mixed with two-stroke oil to the specified ratio. The ratio for some saws will be different but usually somewhere around 30 parts gas to one part two-stroke oil; it’s represented as 30:1.
Your user’s manual will state clearly what the ratio is.
If you deviate from this ratio, the engine may be damaged, and your warranty will be void.
A common problem is putting too much oil in the mix. The excess oil can foul the spark plug when the mix is too strong (too much oil). A fouled plug will misfire and will result in a flooded engine. So now, the excessive gas/oil mix has caused two additional problems, albeit minor. If you suspect your gas mix is way off, just drain the gas tank, refuel to correct mix, remove and clean the plug, and you are good to go.
Thing Two – Your saw must have a good spark and be fired at the correct time. As your saw is brand new, we’ll assume the major components are in great shape, so instead, we’ll direct our attention to some of the more likely causes.
Thing Three – Compression is the engine’s ability to compress air/gas mix. Another way to look at it – is the cylinder airtight? Since your saw is new, we’ll assume the maker did their job right and everything’s in order here.
Diagnosing Your Fault
So far, we’ve checked all the easy-to-cheek stuff; we’re using the correct starting procedure, and our gas quality and mix ratio is good. Let’s also assume for the moment that your new saw is mechanically sound.
That leaves the most likely cause of our no-start – An air-locked fuel system. This is a somewhat common problem with new saws. Obviously, new saws don’t have gas in the system, and so the fuel lines are filled with air.
Your saw uses a rubber diaphragm gasket as a fuel pump; it moves gas from the tank to the carburetor. The pump is operated by the pulsing vacuum created by the cranking/running engine.
Getting the gas to push through the gas lines and force the air out can take several pulls on the saw. Some saws are more prone to air locking than others, but we have a MacGyver-type fix for this, and that’s what we’ll get to next.
Testing & Fixing a Chainsaw Fuel Air Lock
You can test this by first removing the spark plug and checking its condition. A dry plug suggests your system is air-locked. (wet plug suggests an ignition problem or the gas is bad)
But in the workshop, I wouldn’t go to the trouble of removing the plug; I’d go straight for the fix.
The Fix – Remove your air filter and drop a shot of MIXED gas into the carburetor intake (about a thimble full).
Now go ahead and start your saw in the usual way.
Your saw will likely start on the second pull but then stall. Just repeat the process until the saw runs smoothly. That’s it; refit your air filter, and your new saw should start without issue. When running a new saw, allow the engine to warm a little before taking her to full throttle; always be sure you have plenty of bar oil in the tank. Running a saw without bar oil isn’t good for the safety of the saw, the chain, or the bar.
I would advise using a gas stabilizer in your new saw; it will save you a ton of grief in the future. Modern gas laying in equipment is causing gumming of fuel system components. The fuel stabilizer mixed with the gas will prevent gumming, and no starts are associated with medium and longer-term storage.
The stabilizer is not a substitute for 2-stroke oil; you’ll still need to add oil as usual. Here’s a page you may find useful; it’s a list of tools I use when repairing chainsaw fueling systems, including the gas stabilizer – “Chainsaw parts & tools.”
The very best of luck with your new saw.
About the Author
John Cunningham is a Red Seal Qualified automotive technician with over twenty-five years experience working on all types of equipment, grass machinery, ATVs, Dirt bikes, cars, and trucks. When not writing how-to articles, he may be found in his happy place – Restoring classic machinery.
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Chainsaw won’t start after sitting? Stale gas is the number one reason your chainsaw won’t start after sitting idle. Empty out the old gas and try replacing it with fresh gas; if it still doesn’t start, you’ll need to clean your carburetor.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.