Doubled over in pain?
Maybe you have some bad gas.
As for your dirt bike, how do you know if the gas has gone bad? Or maybe you picked up some bad fuel at the prehistoric pitstop with pumps that still mechanically roll the gallons and dollars.
Just like when you have bad gas rumbling through your belly, a dirt bike either stops in its tracks unable to continue or, depending on the severity and pain threshold, sputters along with brief cycles of power… followed by pulling over for a rest.
Bad gas comes from various sources and not just burritos or fecal contaminated lettuce from Mexico:
- Old fuel that has degraded in the tank
- Fuel contaminated by dirt, rust, or debris
- Gas with water in it
- Fuel that sits too long creates gum and varnish deposits
- Poor-quality gasoline
- Fuel unsuitable for the bike or conditions
Generally, those driving their car(s) regularly while hitting up reputable service stations won’t ever encounter bad gas. Take a poll. You’ll likely find more dirt bike riders with harrowing bad gas stories than automobile drivers. I haven’t the time or desire to prove this assumption so let’s go with it! OK, I checked with our resident former pro and he confirmed dealing with bad gas not once but a couple of times when riding his dirt bike.
Most dirt bikers don’t ride every day. Thus, the chance of leaving fuel in the tank longer than necessary rises, plus as the hobby or adventure implies, dirt tends to waft. Remove the gas cap in the pits or on the trail (or simply leave it off for a long period) and expect an infestation of dirt.
Also, most (hopefully most if not all!) of us would never dump the years old, even months old gas from the fuel jug sitting in the corner of the garage in our cars. But the lawn mower? Absolutely. Dirt bike? Maybe definitely.
Common Symptoms of Bad Gas in Dirt Bike
Enjoy troubleshooting on this one. Symptoms of bad gas mimic lots of other problems, some harder to fix than a case of bad gas, while others present an easier solve. But, if you topped off using 18-month-old gas sitting inside a rusted metal can or trusted the M&P convenience store on the outskirts of town, by the railroad tracks where the country moon shines then you might have a gas problem. Check out what could happen when running bad gas in your dirt bike:
- Hard starting
- Not starting
- Rough or unstable idle
- Engine starts, then dies shortly afterward
- Sputtering, coughing, or misfiring
- Hesitation when opening the throttle
- Bogging during acceleration
- Surging or inconsistent RPM
- Reduced power under load
- Stalling at low RPM
- Poor throttle response
- Unusual exhaust popping
- Fuel smell that seems sour, varnish-like, or noticeably different from fresh gasoline
- Cloudy fuel, visible sediment, or water separation (usually seen when drained in a clear container)
- Gummed-up carburetor jets on carbureted bikes
- Restricted injector, fuel filter, fuel line, or fuel-pump flow on fuel-injected bikes
Keep in mind, plugged jets or restricted fuel injectors indicate bad gas from the past not necessarily the current fuel in the tank. And fresh fuel won’t unclog gummed-up anything. (I tried this on a power washer that failed to start along with an abundance of Lucas Oil Fuel Treatment to no avail.)
Also, a dirt bike tuned for higher octane requires high octane gas. Using low octane fuel causes the fuel to detonate rather than burn resulting in knocking.
What To Do If You Suspect Bad Gas
Don’t ride! Shut off the engine and inspect the fuel. If you immediately suspect bad fuel, then likely you already know you were running bad fuel – probably that decades-old stuff in the garage. But if you have fresh gas from a reputable service station then you need to investigate. Look for:
- Cloudiness - indicates water or sediment
- Visible dirt, rust flakes, sediment, or other debris
- Water and fuel separation – Gas floats
- Dark fuel – old, oxidized fuel
- A sour, varnish-like, or unusually stale smell – old, stale gas
- Gummy residue around the cap, petcock, fuel line, carburetor bowl, or injector/fuel-pump area (this indicates you used bad gas previously)
Clean, fresh fuel looks mostly colorless (may have an amber or yellow tint depending on additives) with a bright appearance. Pour the suspect gas into a clear clean container to visually inspect while also letting it sit for a few minutes to determine water contamination and sediment.
Keep in mind moisture impurities - something not readily apparent. This doesn’t come from the gas station, instead, fuel sitting for long periods in a half-filled gas tank or jug along with temperature swings creates moisture inside the tank. Also, ethanol-based fuel loves water and pulls moisture from the air. Stick with pure gas when filling your gas cans for ride day otherwise burn through the ethanol gas within a short period or add a fuel stabilizer.
A cracked or damaged gas cap seal allows moisture to seep inside the tank and a common mistake (learned usually just once) comes from spraying down your dirt bike a little too hard and heavy with the hose or power washer.
Once you confirm bad gas, get it out. With an assistant, turn your dirt bike upside down and let the gas pour out the tank. Jiggle the bike as hard as you can to remove any holdout gas. Just kidding, don’t do any of that. Use some type of suction pump to drain the tank. Drain the carb bowl too, if applicable.
Now, if you’re me, I’m refilling my tank using the best gas possible to dilute any of the bad fuel left behind. Realistically though, a fresh batch of 87 (even ethanol-based) works to get you riding. Don’t leave the gas cap off overnight or even a few hours in an effort to evaporate remnant gas. It’s unnecessary and you open the door to contaminants.
How To Prevent a Case of Bad Gas:
- Rely on reputable service stations
- Use ethanol-free gas / Use “Top Tier” gas
- Use a fuel stabilizer when storing gas for long periods and/or using ethanol laced gas
- Plastic jugs rule the shelves but use a metal fuel can. Fuel stays fresh longer and the plastic ones deteriorate quicker (I can attest to this). Also, don’t leave fuel cans on cold concrete. Instead, store on a shelf or on top of plywood or other wood to prevent moisture.
- Be careful when washing your dirt bike
- Ensure fuel cap has a tight seal and remove only during fill-up
Remember, you are what you eat. Same adage applies for your dirt bike. If you want to fire on all cylinders and not out the tail pipe, use fresh, high-quality fuel manufactured from recognized companies and distributed by trusted stations to keep riding. Lastly, you assume all risk and liability when eating at an unregulated food cart.
Related Dirt Bike Articles
87, 89, 92 or Race Fuel - What Gas to Use in Your Dirt Bike or ATV
Ask a Mechanic: Best Gas for Dirt Bikes and ATVs
Using Old Gas in Your Dirt Bike or ATV
