How to Rewire Your Lawnmower engine for More Power

I want to get more power out of my lawnmower engine so I can improve its performance. There are a few key steps I need to take to rewire the engine properly and safely.

Understanding Engine Rewiring Basics

Before I start tearing into the engine, I need to understand some basics about small engines and rewiring.

How Small Engines Work

Small gasoline engines like those in lawnmowers have a simple design. Here's a quick overview:

So the key components involved in making power are the carburetor, cylinder, piston, valves, spark plug, and crankshaft.

Basic Engine Rewiring

The ignition system provides the spark to ignite the air-fuel mixture. This includes:

To get more power, I may need to bypass or replace some ignition components. But I need to be careful not to exceed the coil's voltage capacity to avoid damaging it.

Evaluating My Engine

Before making any modifications, I should thoroughly evaluate my engine to decide the best approach.

Engine Specs and Condition

I need to look up my engine's specifications, including:

I also need to assess the general condition of the engine. Problems like low compression or air leaks will hamper performance.

Current Performance

I should get baseline measurements of the engine's current performance, including:

Identifying Limiting Factors

I need to identify what's limiting the engine's power output before modifying the ignition. Likely limiting factors include:

Upgrading these components may be required to fully optimize power.

Rewiring the Ignition System

Once I've addressed any issues found during evaluation, I can start rewiring the ignition system. There are a few options depending on the engine.

Installing an Aftermarket Ignition System

I can replace the stock ignition with a high-performance aftermarket system. Some options are:

Bolt-on kits make installation straightforward. I just match the wires from the old system.

Modifying the Stock Ignition

If the engine has points ignition, I can modify that system:

I have to be careful not to exceed the coil's limits with these mods. An aftermarket coil may be needed.

Bypassing Resistance

On engines with a magneto, power can be gained by bypassing internal resistance:

Lower resistance equals more voltage at the plug. But again, I need to watch I don't over-volt the coil.

Optimizing the Rewiring

To maximize the power gains from rewiring, I may need to perform some additional optimizations:

Tuning the Carburetor

With more power, I'll likely need to re-jet the carb for the optimal air/fuel mix:

Retarding Ignition Timing

The extra combustion heat and pressure may require retarding the timing to prevent pre-ignition:

Lower Compression Ratio

Higher ignition voltages can cause pre-ignition on high compression engines:

Testing and Troubleshooting

I need to thoroughly test my engine modifications and be prepared to troubleshoot any issues.

Performance Testing

I should re-test key performance metrics after the rewiring to validate the results:

If I don't see gains, I may need to recheck my modifications or optimize further.

Troubleshooting Common Problems

Some issues that can crop up include:

I may need to install instrumentation like cylinder head temp probes to further diagnose issues.


Rewiring a small engine like a lawnmower can definitely give it a nice boost in power. But I have to be strategic with my modifications and careful not to push components past their limits or else risk damaging the engine. Thorough testing is key to getting excellent performance results. With some smart optimizations to unlock the engine's potential, I can have my rewired mower really tearing up the neighborhood!