CR125
Tech Tips
 

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Recommendations for engine break-in and jetting, as well as what oil and spark plugs to use.  Specifics about top-end, reed and other replacement parts.

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Swedetech Moto - Honda CR125 Tech Tips

Recommendations for engine break-in and jetting, as well as what spark plugs and how much oil to use.  Specifics about top-ends, reeds and other replacement parts.
 

Engine Break-In

Start by increasing the main jet by one to two sizes from what you have determined to be the optimal jetting, taking weather, altitude and track size into consideration.  Always warm-up the engine on the stand and do a walk around of the engine and kart...  Check for loose bolts etc.  Note: Coil and CDI must be minimum of 4 to 5 inches apart.  See specifics below, regarding proper clutch adjustment.

Break-in water temperature should be 140 to 145 degrees, with the normal running water temperature at around 130 degrees (RC20 recommended additive).  You can take the temperature reading anywhere between the cylinder head outlet and the radiator.

Out on the track, run at reduced lap times of 15% to 20% below normal (On a 30 second track, slow the pace by 4 to 5 seconds per lap).  Towards the end of the break-in, gradually increase the pace by approximately 1 second per lap.  Once you're up to speed, you don't have to come in and let it cool down...  Just run it!

Oil

Please call us for recommendations on 2-stroke oil...  Be prepared to advise us what race series that you are participating in and what the "spec oil" is for the series.  Note:  For most sprint racing applications, we recommend a 24:1 mix ratio.

For the transmission, we recommend that you use 650ml of a brand-name 2-stroke gearbox oil if your engine is brand new or freshly rebuilt...  Use 50ml less, for routine oil changes.
 

Spark Plugs

Use any of the following NGK spark plugs...
 

NGK BR10EG NGK BR10EGV (Discontinued) NGK BR10EV

NGK BR10EIX NGK R7376-10

Always add the 2mm washer between the spark plug and the cylinder head, in addition to the stock spark plug washer, on all SwedeTech blue-printed Moto CR125 engines.  Exception:  Do not use a 2mm washer, on an engine that is designed to compete in the FMX class.
 

Top End

Use the following Honda RS piston and ring...
 

RS125 piston - #13100-NX4-780 RS125 ring - #13121-NX4-811

Other top end parts, such as upper-rod bearing, circlips and wrist pin, are stock OEM Honda CR125.  Note:  Always run one base gasket, on each side of the aluminum spacer plate.
 

Jetting - Keihin 38mm PWM

Normal range of jets for a Keihin 38mm PWM carburetor...
 

160 - 180 main 52 - 58 pilot DGJ-DGK-DGL or CGJ-CGK-CGL needle

Start with the needle set in the middle...  Take the time to experiment with the clip in the 2nd and 4th position(s) from the top.

Note:  Even larger jets may be applicable for road racing applications.
 

Reeds

Recommended replacement reeds...
 

142LT - 4-petal straight intake 102LT - 6-petal intake

Clutch Adjustment

You need approximately 3/8-inch to 1/2-inch of free play, at the end of the clutch lever.  Take care not to have more than one inch of travel, once the clutch is engaged, since any more than that might allow the outer plate to jump out of the basket.

Make sure your cables have the nylon inner housing...  Keep them straight and well lubricated.  You should not need more than two fingers to engage the clutch.