How to fix low compression on a dirt bike?

Is your dirt bike facing a problem of low compression? Why does a dirt bike have low compression and what does it mean when this is present? How it will be checked? If all the above questions are creating trouble for you then this article is for you.

Being a dirt bike rider, I have also faced many problems related to my dirt bike, low compression is one of them. So today we are going to share about what is low compression and how to fix low it? when and why you should test engine compression? and how to check it.

What is engine compression?

Before discussing about how to fix low engine this issue you must know about what is engine compression? An engine of a bike is a pump basically. To understand the working of engine you can read how does a dirt bike engine work. In a dirt bike, there are mainly two types of engine.

  1. 2 stroke
  2. 4 stroke

In the process of compression, air and fuel is taken in by the pump and then compresses them under high pressure to start combusting the mixture. By this the mixture gets combusted and it keeps the engine working or running.

You must read what 2 stroke dirt bike engine fuel-oil ratio should be used as proper mixture gives the better efficiency and strength to an engine.

What is low compression on a dirt bike?

As I have already mentioned that here, the air and gas is compressed under high pressure by the engine to start running of the bike, when this issue occurs then the mixture (air and gas) will not burn completely. For finding out the reasons of low compression read the full article.

It is related with the problem start capacity issue. It is also related to the poor beginning capacity characteristics absence of pressure causes this problem.

What causes low compression in a 2 stroke engine?

Piston is used for producing compression in a 2 stroke engine. The pressure is kept inside of the combustion chamber. If the piston of the 2 stroke engine is damaged it will not retain proper compression and the symptoms will follow.

That is why regular check up of your rings on piston is necessary when the compression starts going down.

What causes lowering this in a 4 stroke complications.

4 stroke engine contains rings which are required to be replaced by a new one at a certain intervals. If you do not replace the Rings and valves it will automatically burn out. Damaged valves will cause this issue in an engine.

2 stroke low compression symptoms

The symptoms of this issue in a 2 stroke symptoms are as follows:

  • Problem in starting
  • Low power
  • Bogging
  • Spark plug fouling
  • Doesn’t idle well

4 stroke low compression symptoms

  • Hard to start
  • Kick starter is easy to kick over
  • Back firing/ popping on deceleration
  • Running rough
  • Competitors in power

While checking this issue on your dirt bike, you can find the number of signs and symptoms that indicate that the engine is getting worn out and require attention.

Whether it is a 2 stroke or 4 stroke, it can have this problems. Both type of the engine have similar symptoms but there are some sort of different symptoms than a 2 stroke bikes.

Compression Ratio

It is an important determinant in a motors character. It is the ratio of low much air and fuel can be combusted in an engine to produce the energy.

A compression ratio is basically a type of examination about how much amount of mixture it can sustain in it with comparison to the amount of its base size.

It can also be understood as weight potential. By the process of combustion of air and gas together, it will create tension and the chances of producing more prominent force by consuming air and fuel (gas) exist.

How to do a compression test on a dirt bike

It is very easy to check low or high compression on dirt bike. Checking a this problem on an engine only needs some time. Firstly we will discuss about how to test it on a 2 stroke dirt bike. You only need to follow some simple steps to find this on your stroke dirt bike.

  • Firstly, remove the seat and the gas tank (there are also some bikes which have enough room or space under the tank and it doesn’t required to remove the tank. We will discuss the further steps by considering there is not enough room).
  • Secondly, you have to remove the spark plug from the cylinder head.
  • Thirdly, install the right compression tester of the correct size.
  • fourthly, you have to twist the throttle all the way back.
  • Lastly, pick the pick starter by 4-5 strong kicks (you can only follow this step when you have to test on a cold engine that has not been run in the past 6 hours).

It is very easy to test the this on your dirt bike. Electric bikes also have the same process of testing this. It only requires to hold the bikes starter button for 5 seconds for starting up the engine.


Kindly charge the battery properly to get started easily and for accurate reading too.


Before performing a compression test you must need to check up the following:-

  • Make sure your bike is clean. You have to keep your bike away from the dirt or water. It should not reach to the spark plug or coil pack. It can be a serious problem. It can also lead to severe problems such as scoring of the cylinder, walls, accelerated wear of the piston and rings.
  • Gas should be off at the fuel petcock.
  • The air filter of the dirt bike must be clean and in good condition.
  • If possible, the fuel tank can be removed so that you access to the unobstructed spark plug. You can also inspect the cables and hoses for any other damage.

Choose the best compression tester

So by the above information you are now able to check compression on your 2 stroke/4 stroke dirt bike. Now, the next question is that which tool later would be best for your bike.

Tester is a device filled with lots of hoses and fitting. This test takes less than 10 minutes.

For best compression tester: motion Pro 08-0188 compression tester.

Fixing techniques of low compression

For fixing of low compression problems. For this, you have to buy a pressure measure for conducting pressure test. Once you find the problem of low compression, you need to firstly change the leaking component. These components can be valves, camshaft, cylinder ring, cylinder head gasket.

The main reason for low compression in dirt bike engine can be worn top end. In a top end rebuild on a dirt bike can be done by replacing the piston / piston rings.

In case if your bike is getting old or overheat, and defective parts might be the reason of your low compression issue. The planning belt can also be the guilty part. It is related to camshaft and it is necessary to turn the camshaft.

Minimum compression for 2 stroke dirt bike

An ideal and good compression is near about 150 PSI. If we talk about an 85cc two stroke dirt bike then it should have a minimum compression of 130 PSI to run at a right efficiency and give out better performance.

A balanced and good compression is between 150 and 160 PSI. When we talk about 125cc then two stroke dirt bike should have a minimum of 140 PSI and about 180 with a fresh top-end.


Change all the components of oil leaking. It can result in fixing the low compression. The above discussed article is the detailed explanation of reasons behind the low compression in the dirt bike and how to fix the low compression problem.

I hope this article will be of great help to you.

Thank you !