Technology Information

1999 Honda CR125 Modified Moto Break In Procedures

Courtesy of SwedeTech Racing Engines
(916) 687 – 3980

** Note - This section is for Blueprinted or Modified Honda CR125 Engines built by SwedeTech.  If you are looking for Stock Moto documents, please visit the main tech page.  ** 


The Blueprinted or Modified Moto Engine for karting applications will not run properly on pump fuel (Octane ratings of 87-94). SwedeTech recommends the use of VP Racing Fuel’s C12 product.

Prior to driving on the track, always warm the engine up to a minimum of 110°. While you are warming the engine, do a visual inspection on the engine and chassis for any loose, broken, or misaligned components.

Do Not Run the engine through multiple heat cycles while on a stand. This will not properly break in the piston and ring. The piston and ring will need a load to properly seat. Only run the engine on the stand to bring to proper warm-up temperature (min. 110°), then start your break-in cycle on the track.

On a 30 second track slow the pace 4-5 seconds per lap. Allow the engine to go through the RPM range from 6,500 – 10,500 for the first five laps. At 5 lap intervals, increase rpm’s by 750 – 1000. Continue until maximum rpm’s are achieved. Run the engine at full throttle on the track, keeping rpm’s low by short shifting.


Spark Plug

Shorty Style - NGK R7282-10

Must use the NGK TRS1225 Plug cap with short style plugs

** You must use a resistor type spark plug **
Spark Plug Gap – 0.024” – 0.028”

Transmission Oil

New engine-650ml (21.9 oz)

  • Use 50ml less for routine oil changes ( 20.0 oz )


Two-Stroke Engine Oil

Motul Kart Grand Prix or Maxima 927

Mix 32:1 for break-in and regular use (4 oz. per gallon )

** DO NOT USE PUMP FUEL ** Recommend VP C12


The Stock Moto Engine for karting application will not run properly run on pump fuel. SwedeTech recommends the use of VP Racing Fuel’s C12 product.

Keihin 38mm PWM - recommended by SwedeTech

Jetting range is based on Sprint Kart setup using the SwedeTech GFS system and a 1999 cylinder combo.

165  -185 main ( center of the carb, 6mm hex )
Main jet supplies fuel from ½ throttle to full throttle
62 - 52 pilot ( next to main jet, use 5mm flat screwdriver to remove )
Pilot jet supplies fuel from 0 – ¼ throttle
DGH needle - 3rd from top. Experiment with 4th & 2nd clip from top.
Needle regulates fuel from 1/8 throttle to ¾ throttle
Air Screw ( side of carburetor body, above fuel inlet ) – 1 Turn

Keihin CR125 Jet Kits 

* For new engines purchased directly from SwedeTech and engines maintained by SwedeTech, we offer a jet chart to help customers tune their engine for optimum performance.

Clutch adjustment

You need about 3/8" to 1/2" free play at the end of the lever lifter arm on the engine. You shouldn’t have more than 1 inch of travel when you engage the clutch lever.  When the clutch lifter arm is at rest, it should sit at a downward 45 degree angle.  As you engage the clutch arm, the clutch should start to have an applied load when the lifter arm is at a 90 degree angle to the case or flywheel cover.

Any more than that and the outer plate could jump out of the basket. Make sure your cables have the nylon inner housing and keep them straight and well lubricated. You should not need more than two fingers to engage the clutch.

SwedeTech Quick Tips

Break-in water temperature should be 150° - 155°

Normal running condition water temperature between 125° - 135°

Take the reading anywhere between the cyl. head outlets and the radiator.  Do not place the water temp sensor between the radiator and the water pump 
Engine will lose performance after 135° water temp.

Overheating and engine damage can occur with temperatures past 160°

New engine break-in 15-20 laps.

New Top End break-in 12-15 laps

Increase main jet 1-2 sizes for break-in

RPM Range – 7,000 – 12,700

Top End Maintenance

Top End Kit – Piston, ring, circlips, wrist pin, bearing, head gasket, exhaust o-rings, and base gasket.
For normal use – 6 – 8 hours
For optimum performance – 4 – 6 hours

Normal use – for the recreational racer that is looking for longevity and cost effectiveness. Typical normal use includes jetting the engine on the richer side.

Optimum Performance – for the avid racer that is looking for every performance advantage. Optimum performance includes jetting the engine for best performance.

Note that the above schedule of maintenance is based on our experience. You may find that these times may be adjusted based on your needs, driving conditions, and overall engine maintenance. Many factors affect wear and tear on components.

Lower End Maintenance

Lower end maintenance will require that you send the engine to SwedeTech. We recommend that this service is performed between 30 - 40 hours of use.

Note that the above schedule of maintenance is based on our experience. You may find that these times may be adjusted based on your needs, driving conditions, and overall engine maintenance. Many factors affect wear and tear on components.

Regular Maintenance

 fuel filter and fuel system for debris (Daily)

Drain transmission oil (4 hours)

Rebuild GFS rectangle fuel pump (4 hours)

Rebuild GFS round fuel pump (16 hours)

Drain GFS pulse lines (Daily)

Frequently Used Parts and Part Numbers

Frequently Used Parts and Part Numbers

  • Piston,  13110 KSR 730

Online Store - 

  • Ring,    13121-KSR-731

Online Store - 

  • Bearing, 91103 KZ4 B01

Online Store - 2001 Honda CR 125 Top Bearing

  • Circlip(2), 94601 15000

Online Store - 2001 Honda CR 125 Piston Circlip

  • Wrist pin, 13111 KV3 000

Online Store - 2001 Honda CR 125 Piston Pin

  • Gasket, 12251 KZ4 A91 (2001)

Online Store - 2001 Honda CR125 Head Gasket


  • O-ring, Head - Inner and Outer

Online Store - Modifed and Blueprinted Honda Head O Ring

  • Base Gasket, 12191 KZ4 L10 (2001)

Online Store - 2001 Honda CR 125 Cylinder Base Gasket

We use the 2001 base gasket with both '99 and '01 cylinders

  • Base Gasket, Multiple Thickness Options

Online Store - CR125 Base Gaskets Thickness Options

  • O-ring, exhaust

Online Store - O-ring Replacements for Exhaust Manifold

Torque Specs

Nut, 8mm cylinder head  28 nm, 20 ft / lbs
Nut, 8mm cylinder base 28 nm, 20 ft/ lbs
Stud, 8mm Cylinder (case/head) 12 nm, 9 ft / lbs – apply loc-tite
Stud, 6mm Cylinder (exhaust) 10 nm, 7 ft / lbs – apply loc-tite
Impeller, water pump 12 nm, 9 ft / lbs