New Chainsaw Won't Start

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.

  1. Air locked fuel system
  2. Choke not on
  3. Primer bulb not pressed
  4. Flooded engine
  5. Incorrect gas mix
  6. Bad gas
  7. 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 for free, today.

This stuff is all pretty basic, I promise you won’t need a degree in engineering to apply this knowledge.

Chainsaw

Check fuel system

Chainsaw starting procedure

My father was a mechanic too and when troubleshooting, he thought me to first 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 may have a slightly different starting procedure to previous models you’re familiar with.

All chainsaws will have a on/off switch, choke control, throttle lever and some may have a primer bulb.

You’ll need to check your starting instructions users manual carefully.

A normal starting procedure goes like this:

  1. Check gas tank for fuel level and mixed to correct ratio
  2. Set switch to “On”
  3. Set choke lever to “Full”
  4. Press primer bulb 3-4 times (if fitted)
  5. Pull the starter cord sharply

If the starter isn’t pulled sharply and with some force, the saw wont start. Most saws likely won’t start on the first attempt but should on the second or third attempt.

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 again.

A warm chainsaw may not need choke to start but a cold saw won’t start without choke.

Chainsaw air filter

Check the basics

Pre-diagnostic Checks

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 check list:

  1. Plug wire on and secure (I know for some saws this won’t apply as you can’t access the plug wire without removing a cover which in most cases wouldn’t fit on the saw anyway if the bulky spark plug wire was out of place)
  2. Next I’ll check air filter, I know the saw is new and so the filter is like 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.
  3. Lastly I’ll check the gas. In the majority of cases, the fuelling system is the cause of small engine no starts.

Your saw is new so we know the carburettor 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 with fresh mixed gas. The good gas will make it’s way through the system and push the old gas out.

OK, that’s all the easy stuff checked.

2 stroke oil

2 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 3 things in order 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 users 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. When the mix is too strong (too much oil), the excess oil can foul the spark plug. 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 gas tank, refuel to correct mix, remove and clean the plug and your good to go.

Chainsaw gas mix

Fresh gas

Thing Two

Your saw must have a good spark and 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.

Chainsaws spark plugs

Spark plugs

Thing Three

Compression is at it most basic the ability of the engine cylinder to compress air/gas mix.

Another way to look at it, is the cylinder air tight. But since your saw is new we’ll assume the maker did their job right and everything’s in order here.

Diagnosing your fault

Now we’ll get down to the business end of diagnosing your fault.

We’ve checked all the easy to check stuff, we’re using the correct starting procedure, our gas quality and mix ratio is good. Lets 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.

Why does it air lock?

This is a pretty common problem with new saws. Obviously new saws don’t have gas in system and so the fuel lines are filled with air.

Your saw uses an rubber diaphragm gasket as a fuel pump to move gas from the tank to the carburettor.

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 tank quite a few pulls on the saw.

Some saws are more prone to air locking than others.

Testing & fixing the 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 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 carburettor (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 remains running.

That’s it, refit your air filter and your new saw should start without issue.

Here’s a page you may find useful, it’s a list of tools I use when repairing chainsaw fuelling systems “Chainsaw parts & tools”

Mower air filter check

Gas shot

Related Questions

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 with fresh gas, if it still doesn’t start, you’ll need to clean your carburettor.

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.