Will Mixed Gas Hurt a Four Wheeler? (Don’t do it!)


Putting the wrong gas in your four wheeler is easy to do, mixing up your gas cans happens a ton around here, or maybe you’re short on gas a thought hmmm……

Putting mixed gas in your four wheeler will cause it to smoke like a two stroke engine, but it won’t cause any lasting damage. Try topping up the gas tank with regular gas, which will help dilute the mix.

In this post you’ll learn what effect two stroke mixed gas has on an ATV engine and what you can do to fix it.

Mixed Gas

Two stroke engines as you already know don’t have engine oil like a regular four stroke engine. Instead they use oil mixed with the gas to lubricate and cool the engine.

So using two stroke oil in a four stroke shouldn’t cause any problems. I say shouldn’t because of course your engine and it’s components aren’t designed to handle the oil mix either.

I have done it loads of times and my engine ran just fine and yours likely will too. However problems can arise in the carburetor and ignition system.

Mixed Gas & Your Carburetor

Your ATV carburetor is a finely balanced piece of kit. It’s whole function is to measure, mix gas and air (oxygen) and supply it to your engine.

Running the mix in your ATV can cause a couple of common carburetor problems:

  • Lean running
  • Gumming

What’s lean running? Lean running is an engine that isn’t getting enough gas. Your carburetor works by using the natural sucking power of the piston to pull gas through an emulsion tube and main jet.

The tube and jet are calibrated very precisely.

Trouble is, oil mix isn’t gas and your carburetor can’t tell the difference, so the net result is your engine is running lean.

A lean running engine runs hot and that just isn’t good for the motor, but unless you’re making a habit of running 2 stroke mix, it should be fine.

What’s Gumming? Gumming is a sticky deposit caused by old fuel left in a carburetor. Two stroke mix left in the carburetor for even just 1 month may cause gumming.

The only fix is to remove the carburetor, strip and clean thoroughly. Gumming isn’t a likely problem in the short term and once the mix is flushed through the system, the problem is less likely.

Although all ATV owners should use a gas stabilizer when overwintering their kit. A gas stabilizer will eliminate the possibility of regular gas gumming up your fuel system.

Fouled Spark Plug

Spark plugs may all look very similar but they’re actually very different. Apart from the obvious thread size and insulator length, the plugs have a different heat range.

A spark plug is designed to run hot but not too hot. The plug tip needs to withstand heat hot enough to burn off contaminates like fuel and oil inside the combustion chamber, but not get so hot that it will cause pre-ignition.

Using oil mixed gas in your ATV will obviously coat the spark plug in the oily mix as it enters the cylinder. Your ATV spark plug and ignition system isn’t compatible and may foul up.

A fouled plug stops firing and your engine stalls, continuous attempts to start an engine with a fouled plug simply floods it with gas and compounds the problem.

Removing and cleaning the plug will solve the problem short term.

The Fix

A quick fix – simply top up your gas tank with regular gas, this will dilute the mix and the problem will fix it’s self.

Alternatively, you’ll need to drain the gas tank, and drain the fuel bowl and if the engine has been running, remove and clean the spark plug.

John Cunningham

John Cunningham is an certified mechanic and writer on ATVFixed.com. I’ve been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance, repair to troubleshooting.

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