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How to Build a Racing Lawn Mower Engine

Riding mowers are fun.
Monkey Business Images Ltd/Valueline/Getty Images

Racing lawnmowers is a hobby gaining in popularity. It originated from people tinkering with their stock equipment, creating their own parts and testing their creations against others for fun. With the growing appeal, manufacturers have gotten into the mix, and organized racing leagues have been created with corporate sponsorship. The most important item needed to participate is a great racing motor. The components for building a great racing mower engine are the governor, carburetor, pistons and rods, flywheel, and camshaft. It is definitely worth the expense to purchase durable high-quality parts.

Take out the engine from the frame and body of the riding lawnmower. This will allow easier access to the different sections of the engine to be worked on. It will also allow more room to get the new pieces installed with less difficulty.

Remove the stock flywheel from the engine and replace it with a high-quality billet flywheel. Since the stock flywheel is made of cast aluminum or iron, it is very heavy. The replacement flywheel should be as lightweight as possible using milled aluminum. The engine will now be able to rapidly increase in RPM due to the lower weight and inertia of the flywheel.

Eliminate the governor from the engine completely. The governor is located below the oil pan; it is a brass sleeve where the throttle appears. Remove the sleeve and plug the hole using a washer and nut.

Replace the rod and piston in the engine, as these are precision components. The lawnmower will be running at disproportionate speeds from what it was originally intended to run. The replacements should be composed of billet aluminum to make the engine lighter, stronger and faster. It is important to remember to take precise measurements of the tolerances and fit of the components.

Remove the stock camshaft and replace it with an aftermarket racing camshaft. Racing camshafts have higher ramp speeds and increased lift to open and close the valve more rapidly. Since there are different lawn mower racetracks and conditions, different camshafts may be required at different times.

Replace the stock carburetor with an off-the-shelf racing carburetor. These can be purchased at any local go-kart racing dealers. This new carburetor will remove any limiting factor in the combustion process by improving airflow. With more air coming into the engine, the lawnmower will be even faster.

Things You'll Need:

  • A riding lawn mower
  • Basic hand tools
  • Precision manufactured replacement parts
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