Rough Idle

Power sport is a category of vehicles including ATVs, snowmobiles, personal watercraft, UTVs, and motorcycles, including motocross and trail bikes. These personal vehicles are powered by 2-cycle or 4-cycle internal combustion engines, which may suffer maladies similar to the engine in your car, truck or SUV. 

Many power sport personal vehicles are designed for off-road use and their use may be seasonal in nature. Any engine that is not used on a regular basis, especially one that is stored for an extended period of time, can experience problems with it running properly when it comes out of storage. One of the potential engine issues is a rough, or inconsistent idle speed.

A rough idle may be an indication of a more serious problem that may jump up an bite when you’re riding along a wooded trail, out in the middle of your favorite lake, or enjoying the snow in an isolated spot. Losing power in any of these locations could leave you in a serious predicament. Before this happens, you should address the rough idle problem. 

Causes

Your power sport engine, like other internal combustion engines, needs three things to run properly—air, fuel  and a spark to ignite the air and fuel mixture. If any of these elements are not supplied to the combustion chamber in the proper amounts and at the proper time, your engine will not run smoothly.

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.  

What to Look For

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.

What to Do 

If the fuel in your engine is old, it should be properly disposed of and replaced with fresh fuel. As long as you’re checking the fuel system, remove the gas cap and clean the vent in the cap. If the vent remains clogged, replace the fuel cap.

Your carburetor can best be cleaned and adjusted, and synchronized if necessary, by a visit to a professional mechanic. 

For other items, such as the air filter and spark plug, these can be checked before usage and cleaned, replaced, or adjusted as necessary. If your engine needs new air and fuel filters, or a new spark plug, insist on products from a name-brand manufacturer, such as Champion. Also, make sure that whatever parts you buy are genuine, not low budget knock-offs.      

Results 

Once your engine has been restored to its former self and runs like new, you can enjoy it as it was intended to be enjoyed—off the beaten path without any concerns about getting home safely.

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. We encourage you to consult with a certified technician if you have specific questions or concerns relating to any of the topics covered herein.