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What Should I Do When My powersport Engine Has Rough Idle?


From ATVs and motorcycles to snowmobiles and personal watercraft, there is nothing like spending an afternoon on your powersport machine. An unexpected change in the performance of the engine is cause for concern. A rough or inconsistent idle can be an indication of a more serious problem that could leave you stranded on the trail or water. Address the problem before it gets any worse.



Whether it’s a 2-cycle or 4-cycle gas-powered engine, your powersport machine needs three things to start and run properly:

  • Air
  • Fuel
  • Spark to ignite the air/fuel mixture

If any of these necessary elements aren’t supplied at the proper time and in the proper amount, the engine won’t start.

Most engines use a single carburetor to mix the proper amounts of air and fuel together and direct the mixture into the combustion chamber. Some engines use multiple carburetors to supply the air/fuel mixture to the cylinders. Once the mixture is in the chamber, your spark plug sparks at the proper time to ignite the mixture and provide a driving force to the piston.

A weak or improperly timed spark or incorrect amounts of air or fuel will cause the engine to run unevenly, if it runs at all.



Dirty or Worn Spark Plug(s)
Carbon, oil residue and pitting on the spark plug electrodes will cause a weak or inconsistent spark, resulting in poor ignition and an inconsistent idle.


Dirty Air Filter
A clogged air filter may not allow a sufficient amount of air into the combustion chamber, contributing to a rough idle.


Bad Fuel
Bad fuel will cause your engine to run erratically. Gas can go stale in as few as 30 days, especially fuel mixed with ethanol as it is in many areas. Ethanol attracts moisture over time and the moisture will dilute the gas.  


Dirty Fuel Filter
As with your air filter, when the fuel filter does its job, it will become less efficient and may become clogged, restricting fuel flow to the engine.


Dirty Carburetor
Bad fuel may also cause harmful gum or varnish deposits to form inside your carburetor restricting or clogging vital carburetor passages and jets, resulting in an uneven fuel supply.


Improperly Synchronized Carburetors
If your engine has multiple carburetors, they should be checked by a qualified technician to insure that they are properly synchronized to operate together.



Change air filter if it’s clogged or dirty.


Replace fouled or dirty spark plug(s).


Unclog or replace gas cap if air vent is blocked.


Replace old gas with fresh gas (properly dispose of old gas).


Have carburetor cleaned, adjusted & synchronized.


Learn more about powersport maintenance products, find your part, or find where to buy your part today.

The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

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