Starter fluid is projectile combustion, usually sprayed into the air intake to aid with the ignition process to help your motorcycle start, but why does a motorcycle only start with starter fluid?
If your motorcycle only starts with starter fluid, it’s likely due to a weak ignition spark. That said, there are close to a dozen reasons why your bike’s ignition spark is weak—to make matters more frustrating, the symptoms of these culprits tend to echo one another.
Because of the similar signs, troubleshooting the reasons why a motorcycle only starts with starter fluid can be tricky; we’ve listed the most common explanations below!
Table of Contents
1. Spark Plug Cap; Improper Resistance
If your motorcycle’s spark plug cap produces more resistance than it’s designed to, the additional resistance can hinder the current from entering.
If the cap’s resistance interferes with the surge to your spark plug, your bike won’t start without the extra jolt starter fluid provided.
- To find out if the spark plug cap is your problem, pull the cap off the spark plug and coil wire—some caps pull right off, others need to be unscrewed.
- Once free from the plug, use a multimeter to test the resistance by setting it to read Ohms.
- The ideal resistance range can vary from year model moto to moto, so refer to the service manual for your specific bike. Typically, they say your cap’s resistance should be less than 5,000 Ohms when unhooked and separated from the spark plug.
2. Failing Ignition Coil
Another issue that can cause your motorcycle to have starting problems, like not starting without starter fluid, is a failing ignition coil.
Suppose your ignition coil’s primary or secondary resistance is lower than the ideal range. In that case, your motorcycle will be difficult to start without starter fluid until you replace the worn coil.
Once again, you can be sure your coil is the culprit by testing it with a multimeter.
- First, make sure the ignition is in the OFF position.
- Unhook the spark plug wire from the coil.
- Disconnect the two tiny primary wires from the ignition coil and use the multimeter to measure the resistance between the two terminals. If there’s only one terminal, test the resistance between the single terminal and the ground on the bike’s frame.
- This primary resistance should be 0.2-5 Ohms, depending on the spec range listed in your bike’s service manual.
- Now, test the resistance between one of the coil’s tiny terminals and the spark plug cap (which should still be disconnected).
- This secondary resistance reading should be between 5,000 and 15,000 Ohms, depending on your make and year model moto; consult the more specific range listed in the service manual or have a pro test it to be sure.
3. Your Pick-Up Coil is Faulty
Your pick-up coil is the component responsible for generating the timing signal that regulates your ignition system.
If the pick-up coil is faulty or worn out, the spark plug won’t spark, and your bike will have starting problems unless using started fluid.
- You can test your pick-up coil with a multimeter set to the 2,000 Ohms resistance test selection.
- Test the two wires that run to your pick-up coil and compare the reading to the ideal range listed in the service manual associated with your specific make and year model motorcycle. This range varies from bike to bike.
If your resistance coil reading is 1, you have no continuity, and one of the wires might be damaged. If the resistance rating is higher than the ideal range in the manual, it’s the pick-up coil that’s faulty, and you’ll have to replace it.
4. Problems With the Bike’s CDI Box
Your CDI box is what we call the Capacitor Discharge Ignition unit, the electrical device responsible for regulating a fuel-injected bike’s ignition system.
While CDI box failure isn’t common, overheating and bumpy off-road riding can compromise the soldering on some older boxes, wearing them out in time.
Once worn, a faulty CDI will definitely cause some severe ignition problems, like making it hard for your bike to start without starter fluid.
- Some riders claim they could get their bikes to start without starter fluid by opening their CDI boxes and fixing the broken solders.
- That said, the only true fix for a faulty Capacitor Discharge Ignition box other than to replace it with a new one.
5. Deteriorating/Burned-Out Stator
The stator is the part of your motorcycle’s battery charging system responsible for converting the mechanical energy generated by your motor into a Direct Current the battery can use to recharge while you ride.
Motorcycle stators degrade over time due to engine heat and vibration; some model stators last longer than others, but eventually wear out. Once worn, the battery won’t recharge.
If your motorcycle’s battery isn’t recharging due to a faulty stator, it won’t have enough juice to activate the ignition spark fully, and your bike will have starting problems.
Starter fluid might help get your bike ignited, but with a bad charging system component, you’ll notice your lights and gauge displays are weak, your RPMs are rough, and your engine is occasionally backfiring.
A burned-out stator needs to be replaced.
6. Points Ignition System Out of Tune
Vintage motorcycles used an ignition system utilizing mechanical points.
These points affected ignition sparking and timing. Unlike the low-maintenance, electronically governed fuel injection and motorcycle ignition systems on modern bikes, the points systems had to be serviced regularly to keep the bike’s ignition spark strong.
As the points wear down from usage, the gap distance between them occasionally needs to be reset to maintain standard ignition.
These ignition points could also get contaminated by road debris and corrosion, making maintenance much more significant.
If your ignition points are in poor condition, your motorcycle’s ignition sequence will be off, and your spark will be weak. While using starter fluid might get your bike to start, your points will need to be serviced or replaced if they’re the culprit behind the weak spark, or more engine and ignition problems await.
7. Electrical Wiring Damaged or Frayed
Whether it’s from sitting unused, improper storage, UV rays, moisture, corrosion, flooding, or just general wear and tear, damage to your bike’s electrical wiring harness impairs some critical functions.
If an electrical wire associated with your ignition system is frayed or damaged, your coil might not be getting the 12 volts of battery power required to create a spark. A weak spark will cause your motorcycle to have problems starting without starter fluid.
If your wiring harness is in good condition, the damaged wire might be easy to detect.
However, if all the wires are worn, you’ll have to trace the electrical wiring from your battery to your ignition switch, to the CDI, and to the kill switch.
- Test the wires for internal damage by reading with a voltmeter while you gently tug and shake the wires.
- If the reading changes while you shake the wire, you find the damaged wire that must be replaced.
- Electrical wiring on a motorcycle is more complex the more sophisticated bikes get. There’s no shame in having electrical done by a dealership technician, as it can cause drastic changes to your bike’s ignition and fuel systems that may be irreversible.
8. Undercharged Battery; Contaminated or Loose Terminals
We can’t forget the basics—one of the most common reasons a bike has a weak spark and therefore has trouble starting without starting fluid is if the battery’s charge is low.
As mentioned in a previous section, a battery might lack a charge due to a faulty charging system component, like the stator or the Regulator/Rectifier.
Another reason the battery might have a charge that’s too weak to ignite the spark is that the battery itself is old and expired. All batteries expire eventually, and once they do, they lose their ability to hold a charge sufficient to produce the 12-volt jolt needed to start the bike’s ignition sequence.
- Inspect your battery terminals. If you’re lucky, starting your motorcycle easily without starter fluid might be achievable with a few 90-degree turns.
- Also, inspect the terminal surfaces for corrosion. Rust, dirt, and grime can be enough to interfere with the current transfer, causing your coil to get an insufficient voltage for starting.
- Test your battery with a multimeter set to voltage.
- Hook up to your positive and negative terminals (now that they’re clean) and test the voltage between them.
- The ideal motorcycle battery charge is 12.6 Volts; if it’s less than 12.4 should be enough for a smooth spark without starter fluid.
- That said, if your battery’s charge tests at less than 12.4 Volts, the battery itself may be causing your motorcycle’s starting problems.