Skip to content

Stihl 4-Mix Engines Problems and How to Fix Them

Stihl 4-Mix engines are highly efficient and powerful engines, commonly used in various outdoor power equipment such as chainsaws, blowers, and trimmers.

They are known for their smooth operation and fuel efficiency, making them a popular choice for homeowners and professionals alike.

However, as with any mechanical device, Stihl 4-Mix engines may encounter problems from time to time.

In this blog, we will go through the most common issues that arise with Stihl 4-Mix engines and provide practical solutions to help you get back to work as soon as possible.

Common Problems and Solutions for Stihl 4-Mix Engines

Stihl 4-Mix Engines Problems

Here are the most common problems, we compiled them after reading real users’ reviews and feedback, complaints to the manufacturer customer support, forum posts and etc.

1. Welch Plug Issues

Welch plugs are one of the essential components of Stihl 4-Mix engines that help in maintaining engine compression. When these plugs start to fail, it can lead to several performance issues.

Some of the common symptoms of welch plug problems are a decrease in engine power, difficulty in starting, and increased fuel consumption.

To solve welch plug problems, it is important to replace them with high-quality, OEM parts. This simple solution can restore engine performance and prevent further damage to other components.

2. Ignition Module Issues

Ignition Module Issues

Ignition module problems are one of the common issues in Stihl 4-Mix engines. The ignition module is a crucial component responsible for generating the spark that ignites the fuel in the engine.

When the ignition module malfunctions, it can cause the engine to fail to start or run poorly.

Some common symptoms of ignition module problems include the engine failing to start, running erratically, or stalling.

To fix the issue, the faulty ignition module needs to be replaced with a new one. It is important to use genuine Stihl parts to ensure the best performance and longevity of the engine.

3. Fuel Line Issues


Fuel lines are a crucial component in the functioning of the Stihl 4-Mix engine, responsible for transporting fuel from the tank to the carburetor. Over time, fuel lines can crack, harden, or become clogged, causing problems in the engine’s operation.


If there is a fuel line issue, the engine may not start, run poorly, or stop working altogether. Other symptoms include leaks from the fuel lines, the air in the fuel system, and difficulty starting the engine.


The solution to fuel line issues depends on the severity of the problem. For minor cracks or clogs, the fuel line can be cleaned or replaced. For more severe issues, such as a hardened fuel line, the entire fuel system may need to be replaced. In any case, it is important to diagnose the problem accurately and take action quickly to avoid further damage to the engine.

4. Carbon Build Up on Valves

Stihl 4-Mix engines are known for their power and versatility, but even the best engines can experience problems from time to time. One common issue is carbon buildup on the valves.

Carbon build-up occurs when carbon particles accumulate in the engine, interfering with its performance and efficiency.

This buildup can cause symptoms such as difficulty starting the engine, poor engine performance, and reduced fuel efficiency. The solution to this problem is to regularly clean the valves and keep them free from carbon buildup.

This can be done by using a specialized engine cleaner or by having a professional mechanic perform a valve cleaning service. Regular maintenance and cleaning can help prevent carbon build up and keep your Stihl 4-Mix engine running smoothly.

5. Coil Issues

Explanation of coil problems

The ignition coil in a Stihl 4-Mix engine is responsible for transforming the low voltage from the battery into the high voltage needed to ignite the fuel in the engine. Over time, the ignition coil can wear out and cause problems.

Symptoms of coil problems

Some common symptoms of ignition coil problems in Stihl 4-Mix engines include:

  • The engine won’t start
  • Engine misfires or runs poorly
  • Engine backfires
  • Engine stalls unexpectedly

The solution to coil problems

To solve ignition coil problems in Stihl 4-Mix engines, the following steps can be taken:

  • Check the ignition coil connections and clean them if necessary
  • Check the spark plug and replace it if it’s worn or damaged
  • Check the spark plug gap and adjust it to the correct specifications if needed
  • Check the high-tension lead and replace it if it’s damaged
  • If all these checks don’t solve the problem, it may be necessary to replace the ignition coil itself.

Stihl 4-Mix Engine Troubleshooting Guide

Welch Plug IssuesReplace the welch plug and check for proper installation
Ignition Module IssuesReplace the ignition module and ensure proper wiring connection
Fuel Line IssuesReplace any damaged fuel lines and check for proper fuel flow
Carbon Build Up on ValvesClean or replace the affected valves and ensure proper fuel-to-air ratio
Coil IssuesReplace the faulty coil and check for proper ignition timing


What are the common causes of Stihl 4-Mix engine problems?

The common causes can be improper fuel and oil mixture, lack of maintenance, and old or damaged parts.

How often should I perform maintenance on my Stihl 4-Mix engine?

It is recommended to perform maintenance on your Stihl 4-Mix engine after every 50 hours of use or at least once a year.

What is the recommended fuel and oil mixture for Stihl 4-Mix engines?

The recommended fuel and oil mixture for Stihl 4-Mix engines is a 50:1 ratio of high-quality unleaded gasoline to 2-cycle engine oil.

What should I do if my Stihl 4-Mix engine doesn’t start?

If your engine doesn’t start, check the fuel and oil mixture, spark plug, air filter, and ignition system.

Can I repair my Stihl 4-Mix engine myself or do I need to take it to a professional?

If you are familiar with small engine repair, you may be able to fix simple problems with your Stihl 4-Mix engine. However, it is recommended to take it to a professional if you are unsure or if the problem is complex.

What is the warranty for a Stihl 4-Mix engine?

The warranty for a Stihl 4-Mix engine varies, but typically ranges from 2 to 2.5 years for residential use.


Stihl 4-Mix engines are powerful and reliable tools that can help you tackle a variety of tasks.

However, like all machinery, they are not immune to problems. In this blog, we have covered some of the most common problems that.

Stihl 4-Mix engine users may encounter, including welch plug issues, ignition module problems, fuel line issues, carbon build up on valves, and coil problems.

By understanding these issues, you can take steps to prevent them from happening or quickly address them if they do arise.

Proper maintenance and using recommended fuel and oil can also help to keep your Stihl 4-Mix engine in top condition.

Whether you’re a professional landscaper or a homeowner who enjoys tackling DIY projects, following these tips and guidelines will help you get the most out of your Stihl 4-Mix engine for years to come.

Leave a Reply

Your email address will not be published. Required fields are marked *