Kart Engine Run-in Procedure

Engines need to be run-in after a rebuild to provide best performance and engine life.  Not following the guidelines below could result in significantly reduced engine life or premature failure.

During the run-in procedure, your kart will travel at lower speed than normal.  It is a good idea to put a red cross on the rear bumper to warn other drivers.

Three 10 minute sessions are required. During each session, please keep the engine RPM within the stipulated range.  For example a Rotax in the first 10 minutes should not exceed 8,000 revs and not drop below 6,000 rpm.

At all times, the accelerator pedal should either be fully depressed or fully released. This will help load the engine and result in a longer useful engine life. It will also minimize the buildup of oil on the spark plug and therefore minimize plug fouling.

EXAMPLE – in a Rotax, fully depress the accelerator pedal (to fully load the engine) at 6,000 RPM.  When the engine reaches 8,000 RPM release the pedal. When the engine has slowed to 6,000RPM, depress the pedal again etc.  i.e. do not use partial throttle.  The brake can be used to lower the RPM quicker.

Vic Roy – Engine Builder


Kart Engine Run-in RPM Range

ENGINE OIL Mixture RPM range  1st 10 minutes RPM range  2nd 10 minutes RPM range  3rd 10 minutes
Rotax Synthetic 40:1 6,000-8,000 6,000-9,000 6,000-11,000
Iame X30 Castor 25:1 6,000-9,000 6,000-11,000 6,000 13,000
Iame ReedJet Castor 16:1 6,000-9,000 6,000-11,000 6,000 13,000
Minirok Castor 30:1 6,000-9,000 6,000-11,000 6,000 13,000
Leopard Castor 16:1 6,000-9,000 6,000-11,000 6,000 13,000
Fireball Castor 16:1 6,000-8,000 6,000-10,000 6,000-12,000
Yamah S Castor 18:1 6,000-9,000 6,000-10,000 6,000-12,000
Yamaha J Castor 18:1 5,000-7,000 5,500-8,500 6,000-9,500
CR 125 Castor 20:1 5,000-7,000 5,000-8,000 NA

Process (without a tacho)

Start the engine and drive onto the track. During the first ten minutes of engine run in, the revs should be low, and below the engine power band.   The engine should feel sluggish and not want to accelerate quickly. It is normal for the engine to produce excessive smoke.     Under normal racing conditions, engine operate in the power band.  The engine will feel to have much more power when in the power band.

During the next 20 minutes, the engine revs can be raised slightly higher.  At the end of the run in period (30 minutes), the engine can be fully revved but not before.

The accelerator pedal should either be fully depressed or fully released.  This will help load the engine and result in longer useful engine life.  It will also minimize buildup of oil on the spark plug and therefore minimize plug fouling.

At low revs, depress the accelerator pedal for about two seconds until the engine just reaches the bottom of the power band –  and wants to start accelerating freely.  At this point let the kart slow down to a slow pace again by fully releasing the accelerator pedal.  The brake can be used to help slow the kart down.  Repeat this process.

If the power band is reached, reduce revs.  Generally, you can fully depress the pedal in the tight corners but not on the straights.    

During the next 20 minutes of run in, fully depress the accelerator until the engine just enters the power band. Then allow the revs to slow again.   Repeat this process.

An engine that is over revved during run in will fail or result in shortened life span.

Sometimes, engine can be hard to start as a result of the run in process.  If this is the case, replace the spark plug.

Vic Roy
Engine builder