My MPH is Way Off When I'm Driving

The performance of an ATV or any combustion engine is commonly consistent as long as proper maintenance has been performed. However, occasionally it may appear as if the MPH or top end power of an ATV seems to be slower than an owner might remember. There are a few items that you should consider when you believe that your ATVs MPH is way off when you are driving the ATV.

In regards to engine performance of a small cc-displaced, four-stroke engine, there are two major factors that can (and often will) impact the top end speed or mph of the ATV; the amount of oxygen and fuel entering the combustion chamber and being able to be fully burned, or the application of that horsepower to the rear wheel. Typically, top end speed is caused by a lack of power coming from the engine. There can be an easy answer to this problem or some potentially serious issues that are causing the lack of engine performance.

  • Location of Where You are Riding Occasionally we will bring our ATVs with us on vacation, or for extended trips away from where our typical riding takes place. If this is the case, the location of where you are riding can be a major reason why performance seems to have dropped; especially at higher altitudes along with weather conditions. With higher altitude comes less oxygen, and since a combustion engine needs oxygen in order to mix with fuel to burn efficiently, a reduction in oxygen will result in less power. However, if you're a casual rider, just remember that the higher you climb, the less your motor will be able to breathe; and thus, the less power it will produce.
  • Weather Conditions Just as higher altitude will reduce the amount of oxygen in the air, so can weather conditions. When it's hot and humid outside and the barometric pressure is low, this is another indication of a reduction of oxygen percentage in the air we breathe. When the weather is cool and dry, and barometric pressure is high it means that the oxygen level is higher than normal. This is a reason why many ATV riders notice that their bikes will “slow down” when it's hot and humid, and run very quick when it's cool and dry.
  • Problems with the Engine If weather conditions haven't changed much or you're not riding in higher altitude locations like mountains, then it's likely that the reduction of top end MPH is due to potential engine problems. The most common reason for lack of performance with an ATV is either fuel flow that is restricted, not enough fuel / air mixture entering the combustion chamber, or a loss of engine compression. This could be caused by cylinder head valve seals, piston rings or other potential internal engine issues. On some ATVs there is a MPH sensor that can also be checked. From time to time this sensor can be too loose or too tight. This sensor is located near the back of the motor, located on the passenger side of the gear box that attaches to the rear drive shaft.

  • If you've checked into all of these issues and still can't determine why your ATVs MPH is way off, contact Killer Motorsports or an authorized repair facility for the brand, make and model of ATV you own.


6509 Stephenson Levy Road
Fort Worth TX, 76140