stihl trimmer won't start when hot

Stihl Trimmer Won’t Start When Hot – SOLVED

A weed eater engine is a delicate piece of equipment that requires a good and constant air flow to keep operating. If not, then it could result in the weed eater overheating. Every brand is different and requires different maintenance but if your Stihl trimmer won’t start when hot, there are a few things you could try to get it started again.

Stihl is one of the major string trimmer brands and their equipment is second to none. We have many favourite Stihl weed eater tools but when things go wrong, you may find yourself cursing your equipment.

When you are using a two stroke Stihl string trimmer, the engine has to go through a specific process involving a constant fuel and air flow. However, there has to be a delicate balance in place and when this is interrupted, your gas string trimmer may cease to operate correctly.

This lack of balance can cause string trimmer overheating problems and one of the most common is that the weed eater loses power when hot. The good news is that, in the main, these issues will be simply to fix and can often be done without having to rush off to the repair shop.

Restoring Air Circulation

Having good air circulation is perhaps one of the most important parts of the engine process. This air needs to be cool and will mix with the fuel. However, this airflow could be interrupted for a variety of reasons. Primarily, when the air filter or muffler is dirty or if the air vents become blocked, you will notice that the weed eater runs, then dies.

This is because the air cannot properly circulate around the power system and the fuel will be prevented from moving around freely. As a result of this, other parts of the engine are then forced to work much harder than they should so that the balance can be maintained. Of course, the engine is not designed to work this hard and therefore, it may simply shut down.

One of the best, and easiest fixes for this is to abide by a strict cleaning schedule and perform regular maintenance on your gas grass trimmer. Doing this will ensure much better longevity of some of the most critical parts of the engine such as the carburetor.

Check Fuel Filter And Gas Cap

Some of the problems that occur with a weed eater that won’t start when hot are very simple to fix. It can be easy to become flustered and assume that the issue is something drastic that needs to be addressed by a professional. But before you book in, you should take a look at some of the most simply parts of your string trimmer.

For example, if the fuel filters are dirty, this could result in improper air flow and an improper fuel supply. Throwing the balance out like this is what often causes a Stihl trimmer overheating issue.

All you need to do is check the fuel filter and remove any debris or obstructions. Furthermore, you will need to replace the fuel filter from time to time. The frequency of this will depend on how often the trimmer is used. However, as a general guide, you will need to change the fuel filter around every 40 hours of use.

In addition to this, you will need to check the gas cap. This will give you an indication as to whether the air vent is blocked. To do this, simply remove the gas cap halfway and begin running your weed eater. Doing this will allow any hot air to escape. Of course, you will need to remove any blockages in order to prevent the problem from occurring in the future.

Check The Carburetor

When your Stihl weed eater won’t start, this could be a problem with the diaphragm located in the fuel pump. If this becomes warped, it will no longer operate as expected. As a result of this, the fuel supply will be interrupted and this will prevent the weed wacker from working.

However, this may not be the only issue with the carburetor, there could also be an issue with inlet lever moving out of its correct position. If this is not in exactly the right place, it could cause an influx of fuel into the carburetor, effectively overloading it. In this case, you may need to seek out a professional to perform a service.

Maintain Fuel Supply

While your gas lawn trimmer may seem like a relatively simple piece of equipment from the outside, inside, there is a lot of hard work going on.

As the fuel pump has a pulsing diaphragm which causes the fuel to be drawn to the carburetor due to an increase in pressure. Of course, if there are things in the way, the fuel is unable to enter the carburetor as easily and this will undoubtedly cause problems. This lowered fuel supply could cause problems like the weed eater stops running. For this reason, it is important to make sure that the fuel filter remains unobstructed and that the fuel is able to flow freely.

Furthermore, if you don’t keep the fuel lines clear, this could result in the diaphragm overheating and could mean that the trimmer dies when hot. You may also notice that there are air vents that allow any hot air to escape. However, if these are obstructed, the internal parts may overheat.

Check For Leaks

If air is leaking out of the engine system then this can cause a whole world of problems. As we have discovered, it is important to have a stable flow of air and if there is a leak, this causes a significant interruption and will cause the weed eater to overheat.

There may be several places that an air leak could occur, most commonly, you may find them in the fuel tank or the fuel lines. Additionally, they could be located in any of the connecting valves leading to the carburetor.

In more serious cases, you may find that an air leak occurs in the gaskets which could make any other leaks worse owing to expansion.

Seek A Professional

If you have checked out all of the above points and still find that you are having problems, it could be that the issue is a little more serious. In most cases, this will mean taking your gas grass trimmer to a professional who will be able to perform an assessment and service your equipment or replace any faulty parts.

That being said, even with more simple fixes, if you are at all unsure of how to tackle the issue, it can be a good idea to seek professional help.

Engine Operation

Understanding how your weed eater’s engine works is a great way to be able to solve problems when they arise. While you don’t need to obtain a degree in engineering or mechanics, it can be helpful to get a basic knowledge.

There are four cycle engines and two cycle engines although the latter is much more common in residential equipment. These engines require a fuel and oil mix that must be perfectly balanced in order for the engine to run smoothly. This mix provides a sufficient level of lubrication for the engine.

When you pull the start cord on your trimmer, this triggers a reaction whereby the crankshaft begins to rotate causing a piston to create an intake port for the fuel. When the piston moves up, this creates suction which draws the fuel and oil into the carburetor. Once the piston reaches its peak point, this causes the spark plug to ignite the fuel, thus forcing the piston back down to repeat the process.

Regular Maintenance

If you have a Stihl trimmer that won’t start when hot, the best solution to this problem is to perform regular maintenance on your equipment. Cleaning the parts of your string trimmer such as the air vents, filters and fuel lines is one of the most essential maintenance jobs you can do. However, there are other important things to stay on top of:

  • Regularly replace parts including filters, trimmer line and the spark plug.
  • Inspect parts for damage on a regular basis; be sure to turn off the trimmer and remove the spark plug when doing this to avoid accidental start ups.
  • You should make sure that the idle speed is always correct. If you find that the trimmer stalls when idle, this may solve the problem. However, since you can only adjust this with the spark plug installed, you must wear protective gear.
  • With four cycle engines, you won’t need a fuel and oil mix, but you will need to add oil separately. This should be kept topped up.
  • When not in use, ensure that you store your weed eater in a dry, well-ventilated area.


It is not uncommon for weed eaters to overheat but this doesn’t mean that it is a good thing. You may notice that the trimmer runs then dies due to being too hot. There may be several reasons for this, most of which can be solved at home.

Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.

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