The starter spins the engine at a fair speed, but the engine does not start and the spark is weak or missing. Many ignition systems need close to full battery voltage to make a good spark. A tired battery can still turn the starter, which needs current, but not feed the ignition enough voltage. So the battery is a likely cause even when the engine cranks.
Is it safe to ride?
It will not run. Do not keep cranking: you will flatten the battery further and may flood the engine.
Quick checks first
- Does the starter sound strong and even, or slow and tired?
- Do the headlight and horn work well, or are they dim?
- Is the engine stop switch on RUN, and are the stand, clutch and neutral switches in the right positions?
- Is the battery old, or has the bike stood for weeks?
Diagnose it step by step
1Measure the battery voltage with the multimeter, key off.
- A fully charged 12 V battery reads about 12.6 V or more at rest. Lower, and the battery is weak.
- Low: charge it and try again. Go to Test and charge a 12 V battery.
- Good: go to step 2.
2Does the voltage drop sharply when you press the starter?
- Yes, it collapses to a low value: the battery has little reserve. Go to step 3.
- No, it holds up: go to step 4.
3Test the battery properly.
- Flooded battery: Test a battery with a hydrometer and a load check.
- Sealed battery: take it to a seller with a load tester.
- Weak or failed: charge or replace it: Replace a 12 V battery. A jump start from a healthy battery shows if the battery is the cause: Jump start a motorcycle safely.
4Check for a spark with a tester.
- Make or use a tester: Make a simple spark tester, then Check for a spark safely.
- Strong spark: the ignition is fine. The battery is not the cause. Go to Engine turns over but will not start.
- Weak, orange or no spark: go to step 5.
5Check the connections.
- Battery terminals, earth strap and starter cable ends: clean and tight. See Clean and tighten battery terminals and Do a voltage drop test.
- Still weak: Weak, thin or orange spark.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Flat or weak battery | Low voltage at rest or collapses when cranking | Test and charge a 12 V battery |
| Worn-out battery | Charges, but fails the hydrometer or load check | Replace a 12 V battery |
| Dirty or loose terminals and earths | Warm terminal, voltage lost across a joint | Clean and tighten battery terminals |
| Faulty ignition | Weak spark even with a good battery | Test the ignition coil and plug cap |