What Causes Generator Overcrank? (Causes & Solution)

An overcranked generator is a common problem that can leave you without power when you need it most. In this comprehensive guide, we’ll explore the causes, symptoms, and solutions for generator overcranking so you can get your unit running smoothly again.

When you turn the key to start your generator, you expect it to fire up and start producing power right away. However, sometimes the engine turns over rapidly but fails to start. This is known as overcranking, and it usually indicates there’s a underlying issue preventing normal starting.

Overcranking your generator for long periods can cause serious damage to the starter motor and battery. It’s important to diagnose and address the problem promptly to avoid costly repairs down the road. We’ll guide you through the most common culprits behind generator overcranking so you can pinpoint the cause and take corrective action.

What Causes Generator Overcrank?

Causes of Overcranking

There are a number of issues that can prevent your generator engine from turning over properly and starting up. Here are the most common causes of generator overcranking:

Low Oil Level

One of the first things to check is your oil level. All generators require adequate lubrication to operate properly. If the oil level drops too low, it can prevent the engine from compressing the air/fuel mixture correctly for ignition.

Make sure to check the oil level with the generator on a level surface with the engine stopped. The oil should register between the “Full” and “Add” lines on the dipstick. If it is below the “Add” line, add more oil immediately per the manufacturer specifications.

Fouled Spark Plug

The spark plug provides the electric spark to ignite the compressed air/fuel mixture in the cylinder. If the spark plug becomes fouled with carbon deposits or oil residue, it may fail to spark properly. This prevents gas ignition so the engine turns over without starting up.

Remove the spark plug and inspect the electrodes. If you see heavy black carbon deposits, use a wire brush to gently clean the plug. For minor oil fouling, use an approved spray cleaner. Replace the spark plug if damage is apparent.

Bad Fuel

Using old gasoline with accumulated debris or water can make it impossible for your generator to start. The fuel filters can become clogged, preventing proper fuel delivery. Contaminants in bad fuel can also foul the spark plug.

Drain old gas and debris from the tank and fuel filter if your generator has sat unused for more than a month. Refill with fresh fuel from a clean container. Add fuel stabilizer to keep gas fresh longer when storing your generator.

Stale Fuel

Over time, gasoline breaks down and becomes stale, especially when stored in hot conditions. Stale fuel lacks the volatile compounds required for proper ignition. It can clog fuel systems and foul spark plugs.

If you suspect stale fuel, drain it completely and add new fresh gas. The improved volatility should allow proper starting. Consider adding fuel stabilizer to extend the life during storage.

Clogged Air Filter

A clogged air filter starves the engine of oxygen needed for combustion. This prevents ignition despite the engine turning over. The air filter keeps debris from entering the combustion system. Over time, dirt, dust and other contaminants become trapped on the filter surface.

Check your generator’s air filter to see if it looks heavily coated with particles. Remove the filter and either tap it gently against a hard surface to loosen debris, or use compressed air to blow dirt away. Replace the filter if it’s excessively dirty or damaged.

Dead Battery

The battery supplies the initial electric spark to start the generator engine. Weak batteries lack sufficient charge to engage the starter motor. Attempting to start your generator when the battery charge is low will cause overcranking with no ignition.

Use a portable voltmeter to check your battery charge status. Healthy fully charged batteries register above 12.4 volts. Recharge or replace the battery if voltage is below 12 volts. Make sure battery cable connections are also clean and secure.

Bad Starter

The starter motor is responsible for turning over the engine during ignition. If the starter seizes up or fails to engage properly, the engine may not rotate enough to start. This causes rapid overcranking as the starter motor works hard to turn over a stalled rotor.

Listen for odd noises, grinding or high pitch whining that may indicate a damaged starter. Test starter amp draw and have it inspected or replaced if problems are found. Starters can fail from normal wear over time.

Symptoms of an Overcranked Generator

How can you tell if your generator is overcranking? Here are the telltale signs to watch out for:

  • Rapid cranking that fails to fire up engine
  • Whining or grinding noises from starter
  • Burning smell from overworked starter
  • Lack of ignition even after long cranking sessions
  • Battery quickly draining or showing low voltage
  • Excessive vibration during cranking
  • Reduced cranking speed over time

If you notice these issues when trying to start your generator, there is likely an underlying overcranking problem. Taking prompt action to diagnose and fix it will save unnecessary wear on components.

What Causes Generator Overcrank?

Solutions for Overcranking Issues

Here are the step-by-step solutions to address typical overcranking problems with your generator:

Check and Add Oil

  1. Make sure the generator is on a level surface and the engine is stopped.
  2. Locate the oil filler/dipstick cap and remove it.
  3. Wipe off the dipstick and reinsert it fully into the filler neck.
  4. Slowly pull out the dipstick and inspect the oil level. It should read between the “Full” and “Add” lines.
  5. If the oil level is low, add the recommended oil type slowly to bring it up to the proper level.
  6. Replace the filler/dipstick cap when finished.

Clean/Replace Spark Plug

  1. Remove the spark plug cable from the plug terminal. Use a spark plug wrench to loosen the plug.
  2. Inspect the electrodes on the spark plug. Use a wire brush to gently clean if fouled.
  3. For oil fouling, use an approved spray cleaner and wire brush to remove residue.
  4. Check the spark plug gap spacing. Adjust if needed based on specs.
  5. Replace the plug if excessively worn or damaged.
  6. Screw the new or cleaned plug back into place and reconnect the wire.

Drain Old Fuel

  1. Turn generator fuel valve to “off” position.
  2. Place approved container below the carburetor drain valve.
  3. Open the drain valve and empty any remaining old fuel from the carburetor.
  4. Close the drain valve once empty.
  5. If available, opengenerator fuel tank drain valve and drain old gas from tank into container.
  6. Add fresh high-quality fuel to the generator tank.
  7. Turn fuel valve on and attempt starting generator.

Check Air Filter

  1. Locate the generator air filter housing.
  2. Release retaining clips or unscrew fasteners to access air filter.
  3. Slide filter out and inspect for dirt buildup.
  4. Clean filter by tapping gently or blowing with compressed air.
  5. Replace filter if excessively dirty or falling apart.
  6. Reinstall filter correctly into housing and replace cover.

Charge/Replace Battery

  1. Use protective eyewear and gloves when handling battery.
  2. Remove battery terminals, clean and reattach securely.
  3. Check battery charge status. Recharge if below 12.4 volts.
  4. Replace battery if old, damaged, or unable to hold sufficient charge.
  5. Dispose of lead-acid batteries properly according to regulations.

Test/Repair Starter

  1. Listen for odd noises from starter when cranking. Grinding indicates damage.
  2. Test starter draw by voltage drop. High drop indicates excessive current.
  3. Remove starter and have it inspected or replaced if damaged.
  4. Reinstall starter securely using shims if necessary to realign.

Frequently Asked Questions (FAQ’s)

What happens if I keep trying to start an overcranked generator?

Repeated overcranking may damage the starter motor and drain your battery without successfully starting the engine. This can leave you stranded without power.

How can I prevent overcranking issues with my generator?

Regular maintenance like oil changes, air filter cleaning, battery charging, and inspection of all systems will minimize overcranking issues over the long run.

Why does my generator crank slower over time?

Slow cranking that gets progressively slower can indicate a battery about to fail. The battery may need to be recharged or replaced to restore normal cranking speed.

What should I do if the generator won’t start after cranking?

If the engine fails to start after extended cranking, you likely have an underlying issue like no spark, bad fuel delivery or not enough compression. Seek professional service to troubleshoot and make repairs. Avoid cranking the starter excessively.

Can I damage the generator by cranking too much?

Yes, cranking the starter for more than 30 seconds at once can overheat and damage it. Let the starter cool down for a few minutes between cranking attempts. If it still fails to start, have a technician diagnose the problem.


Generator overcranking usually indicates there is an underlying issue preventing normal starting. Problems like low oil, fuel contamination, battery failure, or starter damage can make the engine turn over without igniting. Following our troubleshooting guide can help you identify and address the specific cause, so you can get your generator running properly again.

Regular maintenance and care will minimize starting problems over the long run. But even well maintained generators can occasionally suffer from overcranking issues due to normal wear. Catching problems early before attempting to crank repeatedly will prevent costly damages. Always have a professional mechanic inspect any persisting starter troubles.

We hope this article gave you a better understanding of why generators fail to start even with normal cranking. Armed with this knowledge, you can diagnose and correct overcranking problems quickly when they occur. Let us know if you have any other generator troubleshooting topics you want us to cover!

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