Why is My Chainsaw Bogging Down? [Easy Fix]

Is your chainsaw bogging down?

Well, you’ve come to the right place because, in this post, I’ll be revealing why your chainsaw is bogging down and how to fix it.

So let’s get straight into it!

Why is the chainsaw bogging down?

Fuel mixture

Two stroke engines run on a mixture of petrol and oil and this mixture has a limited shelf life. If the fuel is left in the saw for an extended period and, by extended I mean more than a month, then there is a particularly good chance that the carburetor will malfunction. 

The carburetor is designed to incorporate an astonishing number of impossible crevices to clean so don’t fiddle with old fuel. I promise the time it takes to replace the old fuel is a mere fleeting wisp compared to the hours of trying to unblock one of the tiny passages in the carburetor.

Check the filter

Prior to filling up with fresh fuel, it is always worthwhile to check the condition of the fuel filter. Normally the fuel filter fits at the end of a flexible tube inside the fuel tank.

The filter is weighted to ensure it remains at the bottom of the fuel tank. Fuel filters are cheap, so it is worthwhile to replace them at regular intervals.

With clean and fresh fuel, the saw should be ready for action provided that the ratio of petrol to oil has been accurately measured.

When manufacturers stipulate a percentage or ratio of fuel to oil they are not offering guidelines, they are being quite specific, and accuracy is required to comply with the suggested ratios. The rule is ‘measure carefully.’ 

If the addition of fresh fuel does not get the engine running purring happily away the next item to check is the spark plug.

Checking for Spark 

Access to the spark plug is normally quite straightforward but care should be taken when removing the connection to the spark plug. Do it gently and carefully, a good connection to the spark plug is critical to the successful running of the engine. 

Once the spark plug has been removed the condition of the plug can be evaluated and normally a little gentle cleaning will suffice but if the plug has serious amounts of carbon deposits more thorough cleaning will be required. 

With a spark and fresh fuel, the engine should start and idle quite happily. All good, but then when the accelerator is pressed the engine dies.

Why does my chainsaw die at full throttle?

In my experience, there are two possible causes of this ‘bogging down of the engine’ and to resolve this the manufacturer’s manual is required or alternatively a little internet investigation.

I would suggest that in the first instance the carburetor settings are checked. In most chainsaws, there are two adjustment settings that control the performance of the engine. The low and high carburetor settings. 

Generally, the manufacturers will specify the required setting in terms of adjusting the screw setting by a turn or two. The procedure works like this and I would start with the ‘low’ screw setting.

Turn the screw completely in and then one and a half or one and a quarter turns out. 

The manufacturer will specify the required turns and, in some tool kits, supplied with saws the screwdrivers have a little arrow on the handle to make it easier to judge the amount of turn.

Once adjusted the engine should idle evenly and there should be little visible exhaust smoke.

Now we are ready to set the business end of the saw.

Moving on to the ‘high’ screw adjustment I would recommend that the same setting be made as to the ‘low’ speed setting. Turn the ‘high’ screw completely in and then a turn and a quarter or half out again.

If the manufacturer’s specifications are available to comply with them however there is another way to make the correct adjustment.

Essentially what causes the engine to die when the throttle is pressed is the lack of fuel getting into the system so by turning the ‘high’ screw out more fuel is allowed into the carburetor.

It is possible to make the correct adjustment with the motor running as turning the screw will alter the speed of the engine and the correct position of the screw can be ascertained by the performance of the engine.

There should not be any lag between the throttle being depressed and the engine revving up.

What to check if the high and low settings have been corrected and the engine still gets ‘bogged down.’

In the annoying situation of the engine still not performing as required after the settings have been corrected then I would suggest an inspection of the exhaust system. For this, the removal of some of the outer casings will be required as the exhaust will need to be opened up.

What can go wrong with the exhaust system?

There are two main suspects in this investigation. Firstly, many exhaust systems have a deflector plate that sends the hot exhaust gasses away from areas where the heat may cause some damage.

And the second suspect is the spark arrestor which is a safety device that helps prevent the chainsaw from causing fires while being operated.  

The deflector plate can get carboned up mainly because of a too rich fuel mixture, so a gentle removal of the deposits is required. Normally a scraping down with a flat screwdriver will remove the offending carbon and oil deposits and correct the situation.

The spark arrestor grating is a little more difficult to clean, however, as it is relatively delicate. Do not be tempted to discard the spark arrestor. It is an important piece of safety equipment on the saw.

Rather a spray can of carbon cleaner gets the grating back to a pristine condition. Do make sure when reassembling the exhaust deflector plate that the direction of the exhaust gasses is correct.

One more step before the job is complete.

One last little check is to make sure that the air filter is clean and in good condition. Add this to your checklist when sharpening the chain. A correct fuel mixture together with a clean air filter will ensure a clean and efficient exhaust system. 

So hopefully now the chainsaw is running perfectly and cutting easily. The next time the chain is sharpened, take time to thoroughly clean the saw.

For this, it may be necessary to remove the cover over the chain drive to get to all the bits and pieces that if left there, will cause the machine to overheat.

Why does my chainsaw stall when I give it gas?

Chainsaw loses power when hot

Conclusion

So that’s how you fix your chainsaw bogging down.

Hope you found what you were looking for in this guide.

Happy sawing!

– Adam