Stihl trimmer cords can be hard to pull once pressure builds up in the engine. Fortunately, everyday users have found several methods to fix the issues and get you back to work.
Stihl trimmer cords become hard to pull when pressure mounts inside. That happens with blockage, too much fuel, temperature cycling, or carbon buildup. For these, you can clean filters and mix better oil and fuel. Otherwise, you want to unplug and pull the cord to clear the chambers.
Here are some ways to tackle a Stihl trimmer once the cord becomes hard to pull.
Reasons Your Stihl Trimmer Cord Is Hard To Pull
Before investing in more time-consuming efforts, there is some troubleshooting you can do.
When pressure builds up in the Stihl trimmer’s engine, you may find yourself trying too hard to get it started.
You may have tried to hold the shaft down with your foot to keep it down while you pull the cord as hard as you can. It takes several tries, but you finally get it started.
Otherwise, it can be as bad as only being able to pull the cord a few inches. The whole engine will move with it and refuse to let you hold it down.
When this happens, it can be challenging to determine the source of the problem. Stihl trimmers have many moving parts that need proper maintenance, and pinpointing the small component causing the issue might seem impossible.
However, when one of these trimmers malfunctions or becomes too difficult to use, you might have one of these issues:
The Fuel Compression Levels Are Not Ideal
High compression is the most common issue for a malfunctioning or difficult-to-use Stihl trimmer.
Fuel gets into the crankcase, which builds up pressure when this happens. Sometimes, the pressure can get so high that it becomes challenging to get the engine to turn over.
This push happens most when there’s too much fuel or temp cycling.
The machine has a one-way valve for air to get in but not out. So if temperature cycles apply to the tank, the air warms and cools, thus expanding and condensing. The condensation stage sucks in more air and creates more pressure. Then, the pressure pushes the fuel to the crankcase.
The Piston Head Has Carbonized
Small engines often need adjustments to the carbonation as they don’t have a compression release.
Without these adjustments, the ring will gunk up, and the combustion chambers will develop heat spots. These heat spots can create blockages in the chambers, preventing the compression from regulating.
The Valve Lash Is Malfunctioning
As a last resort, you can check under the valve cover to see how well the valves function. Both valves should open and close.
Compression release needs the valves working to their fullest extent, opening all the way and frequently. The valve lash determines this. Excess lash can limit how well valves operate.
The Tooth Blades Have Moved Out of Place
You can also check the tooth blades’ offset if the torque seems low. Some blades won’t work well if they are off even by 0.005 inches (0.013 cm). When these blades are in the incorrect position, they might build up so much friction that they get hot and jam up.
There Is a Blockage in the Stihl Trimmer
Some other simple issues you can check for are:
- Restriction to the air cleaner
- Restriction to the exhaust
- Signs of the liberal use of two-stroke oil
These three problems can cause resistance and only need quick cleaning. The latter can clog the muffler.
5 Ways To Fix A Stihl Trimmer Cord That is Hard To Pull
So, now that you are more familiar with the many things that can go wrong with a Stihl trimmer, let’s look at some quick and easy fixes that could get you and your trimmer up and running again:
1. Check for a Compression Issue
One helpful approach that you can add to any troubleshooting effort is to turn off the switch and pull the cord when the machine is unplugged. Usually, in compression issues, the parts move freely if unplugged.
While it’s unplugged, you can check the cylinder. Sometimes it collects heavy carbon on the piston head. More on that later.
Also, too much fuel can be in the crankcase, preventing fuel compression. The lack of fuel compression makes the engine pressure too compressed to turn over.
Otherwise, keep it unplugged and remove the spark plug. Loosening it enough to let air and fuel out is also doable.
Pull the cord all the way several times with the choke off and the throttle open. Pulling under these conditions lets the machine work through old or excess fuel and let it out through the spark plug hole. Keep at it until no more ejects from the spark plug hole.
Wipe down and insert the spark plug again. Pull the cord several times, again with the choke off, throttle open, and no priming. This process gives you the chance to notice when the engine uses the fuel in the cylinder. Eventually, the cord should pull easily.
Once it pulls with ease, you can start the engine. Starting works best if you have the optimum mix of oil and fuel.
If you still have issues, recheck the spark plug. You sometimes have to repeat the process if the plug is covered with fuel.
2. Decarbonize the Piston Head
Use premium synthetic oil and run it 50:1. Also, empty any old fuel and add fresh. Low-grade mix oil, especially after lots of use, encourages carbon buildup. So premium mix oil can save you lots of trouble.
Decarbonizing fluid can also help.
3. Adjust the Valve Lash
This issue happens a lot with four-mix motors, and such products used to come with gauges and rocker cover gaskets. These days, a cord that’s hard to pull is a prompt to check for an excessive lash.
Stihl dealers also sell feeler gauges and rocker cover gaskets specific to trimmers separately.
4. Adjust the Tooth Blades
Recalibrating and adjusting the tooth blades might get your Stihl trimmer up and running again.
To recalibrate the blades, check for areas where they might have jumped out of position. Find the torque bolt on the top of the flat metal piece that holds the blades in place, and be sure that it is tight but not too tight. It should be firmly in place but not so tight that it is impossible to adjust by hand.
You may also want to look for blockages around the blade, such as clumps of mud or sap. If you find any, brush them away with an old toothbrush, wire brush, or anything else you might have lying around.
For a more in-depth look at how to adjust and work with the blades, check out this Youtube video from Dan’s Vlog:
5. Clean the Trimmer
A buildup of sap, dust, and other gunk can clog up the airflow in your Stihl trimmer, making it difficult or impossible for the device to start.
So, while you investigate other potential issues, use a brush or cloth to clean off the trimmer and check for obstructions in the exhaust, air valves, and anywhere else that you see debris buildup.
Stihl trimmer cords often become hard to pull when it gains too much pressure. They develop that pressure when the airways get blocked, have too much fuel, go through temperature cycling, or have carbon buildup.
To tackle any of these pressure causes, you have options. For blocked airways, you clean filters. If you have too much fuel or need better mix oil, you can empty the chamber and add what you need. But in stubborn cases, you want to unplug the trimmer and its spark plug and pull the cord repeatedly to clear the chambers.