No fuel equals no fun. Not to worry, as dirt bike problems go, a lack of gas flow is one of the easier and cheaper ones to fix. You are in the right place, I’m a mechanic with twenty-five years experience and I’ll bet you’ll be riding shortly.
The top six causes of a lack of dirt bike gas flow include:
- Blocked tank vent
- Blocked gas filter
- Blocked gas tank
- Carburetor adjustment needed
- Faulty fuel pump
- Mechanical issue
In this post, you’ll all the common reasons a dirt bike isn’t getting fuel. You’ll learn how to diagnose your problem and how to fix it right now.
Dirt Bike Fuel System Types
Before we get into the diagnosis of the root cause of no gas flow it’s important to know which type of fuel system your bike has, not all dirt bike fuel systems are identical.
Dirt bike fuel systems come in two flavors:
1 – Computer controlled fuel injected system
2 – Carburetor gravity feed fuel system
Because these systems are similar but not identical, the possible causes of no gas flow are also slightly different in places.
What’s the difference between the two fuel systems?
Both systems employ some similar components:
|Carburetor Gravity Feed System||Fuel Injected System|
|Gas tank||Gas tank|
|Gas filter||Gas filter|
|Throttle position sensor|
Carburetor Gravity Feed System – These types of fuel systems are typically in all older bikes and employ a mechanical carburetor that mixes air with gas. The gas is fed to the carburetor from the gas tank using only gravity. And that gas is held in the carburetor gas bowl (reservoir) and stands ready to feed the engine as needed.
Fuel Injected System – This type of system as you know employs some of the same components as a carburetor type but it is a way more sophisticated system. It employs sensors, solenoids, motors, and a computer to mix air and fuel and delivery it to the intake system. Some dirt bikes may require a battery to run the fuel-injected system and others don’t.
It’s a pressurized system and uses an integrated gas tank fuel pump to both move the gas from the gas tank quickly and to pressurize it.
How to identify which type you have?
Not always that easy to spot the difference without removing some covers and components. Often it’s better to check your owner’s manual or google search your model.
Diagnosis No Gas Flow
Now we’ll get down to the nuts and bolts of diagnosing where your fault lies. We’ll run through each of the likely no-fuel causes and I’ll indicate in advance if it’s applicable to carburetor or fuel injected or both type systems.
We’ll run through all the easy-to-check likely causes first, no sense removing seats and covers unless we need to.
Blocked gas tank vent (both carburetor and fuel injected)
Gas tanks need to breathe, meaning as the gas leaves the tank it must be displaced by air otherwise the flow of gas stops. This is true for both carburetor and fuel-injected systems. As you know the tank is vented through the gas tank gas cap and attached hose.
Diagnosis – We start with this test as it’s likely the easiest test of all. Gas caps get lost and are sometimes replaced with a makeshift cap and for many, that’s where the problem begins.
The gas tank vent could equally be at fault so to eliminate both the gas cap and the vent hose from the list, go ahead and remove the gas cap and attempt to start the bike. If gas now flows to the engine, you found your problem.
The fix – Replace the gas cap and vent hose.
Blocked gas filter (both carburetor and fuel injected)
Gas filters are fitted inline, some at the gas tank others may be carburetor integrated. A filter’s job is to catch the debris in the gas tank and prevent it from reaching the engine’s intake system. Gas filters should be replaced or cleaned once a year, many aren’t.
Diagnosis – Locate the gas filter and check for debris. Clear inline filters are the easiest to check. Removing the fuel line downstream of the filter (carburetor side) and checking flow is a fast way to eliminate a filter issue.
The fix – Clean or replace the gas filter. When replacing clear bottle gas filters, the filter arrow points to the carburetor.
Blocked gas tank (both carburetor and fuel injected)
A blocked gas tank isn’t hugely common anymore, plastic tanks have removed the corrosion issue associated with metal tanks. That said, a poor flow from the tank may well be caused by a tank blockage. Re-gas from contaminated refill cans can easily introduce debris.
Diagnosis – Removing the gas cap and peering in likely won’t reveal much. The best approach is to remove the gas line at the gas tank and check flow. A poor flow means you’ve found your issue.
The fix – If you suspect tank blockage, you’ll need to remove the tank to clean it thoroughly. That will mean removing the seat, side covers and removing the gas lines and tank fasteners. Once removed, turning the tank upside down will remove the debris. Rinse out using fresh gas.
Carburetor adjustment needed (carburetor)
A fuel starvation issue may be caused by a maladjusted carburetor float. The float’s job is to help control and maintain gas flow in the carburetor bowl. As its name suggests the float floats on the fuel inside the fuel bowl. The bowl is a reservoir of gas that stands ready to feed the engine.
As the engine uses gas, the float drops which allows more gas to flow in to replenish the spent gas. If the float tab is set too high, the bowl won’t fill.
Diagnosis – Remove the gas bowl and check the float level. You’ll need a caliper and the float spec for your engine.
The fix – Adjust or replace the float and valve needle.
Faulty fuel pump (fuel injected)
A fuel-injected system employs a gas pump located inside the fuel tank. Its job is to pressurize the gas and move it to the engine. Fuel pumps work hard and do fail a lot. A failed pump is for some easy to identify as a fuel pump emits a buzzing noise when in operation. That said it is possible for a fuel pump to emit a buzzing noise but not build sufficient pressure to feed the engine.
Diagnosis – To test a fuel pump thoroughly we’ll need to check fuel pressure and to do that we’ll need a fuel pressure test kit. A good pump will typically build pressure in the region of 45psi.
There are still some tests we can do without a fuel pressure test kit but we will need a DVOM. We can check pump resistance and to do that we’ll need to access the gas tank. That will mean removing the seat, side covers, and air intake.
Test fuel pump resistance gain accesses to the injector and check the electrical connector is secure. Now go ahead and remove the connector and set it aside. Using the DVOM set to ohms (Resistance) probe both terminals gently and note the meter reading of about 6 ohms works. If you measure excessive resistance or open, you found your problem.
The fix – Replacing the pump isn’t difficult, You will need to be careful when removing the fuel line connector, often brittle and when fitting the new pump the O-ring seal will require some oil.
Fuel injector faulty (fuel injected)
The fuel-injected system employs a fuel injector to spray a fine mist of fuel into the intake system, without the injector activating we won’t get fuel to the cylinder. To test the injector, we can check it for resistance, and do that we’ll need a DVOM.
Diagnosis – Access the injector and check the electrical connector is secure. Now go ahead and remove the connector and set it aside. Using the DVOM set to ohms (Resistance) probe both terminals gently and note the meter reading.
A reading of about 12 ohms indicates a good injector, outside this, and you’ve found your fault.
The fix – Replacing an injector is a simple process. Remove the electrical connector, fuel line a couple of fasteners, and it off. When replacing the injector, lube the O-ring to aid fitting.
Mechanical faults (carburetor)
Since a gravity-fed fuel system relies on gravity and engine vacuum to draw gas into the engine, compression, therefore, may cause a fuel flow issue. A lack of compression to most engine owners sets alarm bells, but it should be noted not all low compression issues are serious.
Common non-terminal low compression issues include:
- Valve adjustment required
- Loose spark plug
- Head gasket leak
- Valve seat wear
Diagnosis – I’ve covered compression issues and testing previously and you can check that post, right here “Dirt bike with low compression”
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John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.