Motorcycle Won’t Start & Smells Like Gas (Solved & Explained)

The garage door is opened, the sun is shinin’, and you’re all geared up and ready to go, but when it comes time to crank her up and turn her over, nothing happens; your motorcycle won’t start.

As soon as you start tinkering around to troubleshoot, you swear you smell gas.

If this problem-combo rings a bell, you’ve come to the right place. Here are 9 reasons a motorcycle won’t start and smells like gas!

1. The Carburetor’s Float Needle Is Stuck

Let’s just get this out in the open right now—fuel-issue-inspired no-starts are way more common on carb bikes than on fuel injected motorcycles, though you will see some things on the list that apply to both.

That said, this first topic is for the carb-powered crushers; if your carburetor float needle gets stuck, your bike will smell like gas.

  • Your float needle governs fuel flow from the carb to the motor.
  • With use, which is especially true if it’s been a while since you’ve cleaned out your carburetor, road grime and fuel gunk can jam up your carb.

If corrosion or debris build-up in your carburetor, your float needle can get stuck in the open position, allowing gas to flow down to the engine without regulation. Not only does it cause the bike to smell like gas, but it also has the potential to flood the engine with fuel, preventing it from starting. 

This is a pretty cut-and-dry situation to rectify, so we put it high up on our list.

There are a few ways to find out if a stuck float needle is why your bike won’t start and smells like gas; let’s start with the one that doesn’t require disassembling your bike’s carburetor.

  1. Inspect the bottom of your carb.
  2. Look around for a drain hole.
  3. If fuel is leaking from the carb’s drain hole, you’ll at the very least need to clean out the carb; chances are the float needle is stuck and leaking fuel into the motor, flooding the engine so the bike can’t stop and making it smell like gas.

Oh, and this is important:


Your engine cylinder could be full of leaking gasoline, depending on how long it’s been sitting and spreading. Pull the plugs and turn the crank by hand to force all the fuel out of the engine cylinder, then clean and rebuild the carb.

Next step?

Check the condition of the petcock, which brings me to our plan’s next item…

2. Your Bike’s Petcock is Clogged

A clogged petcock is another likely cause of a staunch fuel stench on a motorcycle that won’t start.

The petcock is a valve used to control the fuel flow, with adjustment settings to allow the rider to turn the fuel on and off and activate the reserve fuel tank when your primary tank is empty.

One of the most common causes of this moto-mishap combo is a clogged petcock, making it one of the first few things to check.

Most petcocks use a tin screen filter to prevent fuel slop from clogging them.

Over time, the filter can become clogged or even corrode and let unfiltered fuel inside.

If it’s as simple as unclogging your screen, you might be able to make do with a quick shake, attempting to use the force of motion to dislodge the screen-clogging gunk.

If the block is bad enough, if the screen isn’t working or damaged, go ahead and deep clean the whole petcock and replace the filter asap.

3. The Fuel Tank, Lines, Or System Are Leaking

Another early stop on the troubleshooting train should be checking for leaks from the actual gas tank. If the tank is all good, make sure it’s not the fuel lines themselves that are losing fuel on their way from the tank into the carburetor.

  • Examine your fuel tank first, making sure it isn’t simply overfilled, though most bikes have an overflow vent that spits out any excess fuel during the filling process.
  • If the tank isn’t overfilled or can’t be overloaded thanks to said vent, check the tank for leaks.
  • If you’ve already cleared your fuel tank as leak-free, move on to the fuel valve. 
  • Also, check the connection directly under the tank, where the fuel lines connect; secure any sketchy connections.

Any damaged fuel lines or connectors need to be replaced immediately.

I see you out there, all my rat-bike roasting siblings; look, I’m all about the DIY fixes, but there’s no patching a hole in your fuel system unless you’re stranded on the side of the road, trying to get to the nearest place that sells moto-fuel systems.

Suppose the problem was leaking connection points. You might be able to fix it by fastening its clips.

If a leaking valve is an issue, you can try to rebuild the valve., if it’s not too severe, we’d probably suggest just replacing the part and starting with a new fuel system.

Related: 10 Ways To Make Your Motorcycle Run Smoother (SOLVED)

4. Your Motorcycle’s Spark Plugs Are Worn Or Damaged

Spark plugs are those rubber-boot-protected little engine screw-ins responsible for igniting the air/fuel mix as it flows from your carburetor or shoots from your fuel injector.

Bad spark plugs fire out of sequence, causing frequent misfires to occur.

A misfire happens when the fuel enters your combustion chamber without igniting.

If your spark plugs are damaged or expired, they’ll fail to light your air/fuel mix, causing the uncombusted fuel to flood the motor.

This causes the fuel smell we keep bringing up, but a flooded engine can also be impossible to start.

Bad spark plugs can leak so much uncombusted fuel it leaks out of your exhaust.

  • You can quickly check your spark plugs’ condition if you know where they’re located. Take a quick peek at the owner’s manual if you don’t.
  • Pop the plug out of its socket, carefully following your moto-manufacturer’s instructions, and look at the tip.
  • Your spark plugs should be golden brown; it’s done for if it’s white or black.
  • Also, inspect the plug’s gap distance. If the gap has closed up or widened or the plug’s tip has shortened, the plug needs to be replaced.

All spark plugs wear out eventually, so inspecting them is part of routine ownership maintenance.

Your bad plugs could be the casualty of another problem, possibly with the bike’s air/fuel ratio.

If your spark plug isn’t worn from being old but damaged due to an air/fuel problem, your replacement plugs will be injured. 

If this is the case, you’ve more troubleshooting ahead.

5. Your Air/Fuel Mixture Is Running Too Lean

Running leans means your air/fuel mix has too much air and not enough fuel. Therefore, your bike runs lean on fuel, even though there’s plenty in the tank.

A lean fuel mix can turn your spark plugs and even your exhaust pipes white or light gray.

You’ll also notice backfiring while you’re throttling down.

A lean fuel mix is usually the product of poorly fitting aftermarket air or exhaust enhancements. 

Too much air can also be caused by installing the wrong side carb, or your carb float’s fuel level is set too low.

While you can adjust some carbs via a fuel adjusting screw that governs the air/fuel mix, others have a screw that adjusts the airflow rather than the fuel.

If your bike’s adjustment screw doesn’t do the trick and you know that lean air/fuel mix is your problem, you might have a leaking air filter or manifold— hang tight, I’ll get there.

Related: 5 Reasons Motorcycles Misfire When Hot Or Cold (Explained)

6. Your Air/Fuel Mixture Is Too Rich

If your bike’s air/fuel mix is delivering too much fuel and not enough air, we say the bike is running rich.

Converse to the lean symptoms, the rich mixture will cause your spark plugs and pipes to turn black and sooty.

It also causes the bike to idle sporadically.

Finally, a motorcycle with a rich air/fuel mix will smell like gas and have problems starting.

  • The most common culprit is a clogged air filter; dirt will prevent the proper amount of air from reaching the combustion chamber.
  • Another frequent cause of a lean mix, once again, is aftermarket upgrades that don’t fit right, aren’t installed correctly, or are just plain intended for use on a different size or type of bike (I swear I’m not picking on you rat bike-builders—it be what it be).
  • And finally, it might just be that your float’s fuel level is set too high—fingers crossed.

7. Your Carburetor Is Poorly Adjusted

If your carb is out-of-whack, likely because that air or fuel screw we talked about two sections ago is set incorrectly, your carb balance can cause the fuel mix to run rich, lean, or leak fuel, making the bike to smell like gas and causing some problems starting. 

On a carbureted motorcycle, each engine cylinder has its carb.

If one carb is off, the cylinders aren’t working in sync; the performance gets sporadic, the fuel economy dips, the bike stalls and has trouble starting, and the bike smells like gas.

Rectifying this issue is often as simple as adjusting the carb out of sync, either via air screw or fuel screw, depending on your specific make and model.

A carb can get thrown out of sync from a poor tune-up or the general vibration of the bike.

Related: Motorcycle Stutter When Accelerating? Here’s Why (SOLVED)

8. Your Vacuum Lines Or Air Manifolds Are Cracked Or Damaged

If the vacuum lines transporting fuel crack, rot or incur harsh treatment from being a road warrior, your bike will develop problems starting and will smell like gas.

As mentioned earlier, the same thing can happen if your air manifolds leak.

Like with the fuel lines, if your manifold is cracked and leaking, you can patch it to get you where you need to go if you are stranded; we recommend replacing the leaking lines and manifolds asap to prevent long-term engine damage.

9. The Motorcycle’s Ignition Timing Is Off

If your bike’s engine timing is thrown off, your plug will fire at the wrong time, failing to ignite your fuel on its way into the combustion chamber.

The unburned gas will start to evaporate through the airbox, causing the gas smell to haunt you.

Eventually, if it goes unchecked, these unaligned spark-plug firings can result in a flooded engine, causing the bike to stall out and giving you problems with firing her up.

If your engine timing is off, take it easy on the bike until you get where you’re going to prevent engine knocking that can cause some severe damage.

You’ll need a pro to take a crack at it for poor engine timing, which is why it’s way down at the bottom of the list.

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