If your dirt bike has low comporession then there is still a chance it will start depending on how much compression your bike is producing. Different dirt bikes vary but you will need to carry out a compression test and get a reading above 100 psi for the smaller sized dirt bike and more than that for larger bikes.
If your dirt bike is losing compression then you need to get it fixed as it can result in further damage to your engine which will end up costing more. Low compression will not fix itself.
In this post I will talk about the following topics
- How do I know if my dirt bike has low compression?
- Symptoms of low compression
- How do you fix low compression
How Do I Know If My Dirt Bike Has Low Compression?
The only accurate way of testing your dirt bike for compression is using a cylinder compression gauge. The gauge will provide a reading in PSI showing the amount pressure your cylinder is putting out.
If your bike will start then to get a true reading you should start the bike and allow it to come up to running temperature. If it wont start then the reading will be a little under so allow for that in your results.
To use the cylinder gauge you remove your spark plug and replace it with compression gauge nut to carry out the test . On the other end you attached the hose which has the reading dial on it.
With your bike throttle fully open you need to either hit the electric start if you have one, if not pump the kick starter. When the needle on the gauge doesn’t move any higher you have reached the maximum reading and that is your result.
Compare the reading to your service manual to decide if you have low compression. To give you an example my 1991 Honda XR250 manual tells me I should have a PSI reading range from 185 – 213.
When are taking the reading it is also important to note that you want to observe the needle moving upwards in a nice even motion but quickly. If it doesn’t then it could be a sign that you have worn components.
Symptoms Of Low Compression
- The kickstarter kicks very freely with no resistance
- The bike wont start
- If the bike does start you may experience lose of power
How Do You Fix Low Comspression?
You fix low compression by finding and mending the pressure leak. Low compression occurs when the pressure your bike creates to enable it to run, starts building up in your cylinder but is then able to escape before it reaches the required PSI.
Fixing low compression will be different for 2 stroke bikes and 4 strokes bikes. On a 4 stroke tit is more complex and even if you have done a compression test you will not be able to accuratley pin point the issue.
For this reason a 4 stroke dirt bike will need a test known as a leak down test. You need a leak down testing kit and knowledge of how to use it but essentially you are again pressurising the cylinder and then listening out for air leaks in certain areas to establish where you may have a leak before taking everthing apart. Personally I take it to someone else to test.
A 2 stroke dirt bike will likely be fixed with a top end rebuild, this includes the piston and rings.