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The 50cc carb also has an “automatic enrichment valve” mounted on the right side. This
valve feeds both fuel and air to the engine side of carb slide. It is designed to maintain
stochiometric metering, admitting both fuel and air. This valve is an electronic solenoid
that moves in or out based on a signal from the stator or the CDI. If the unit has no
movement, the unit has failed, and must be replaced.
Common problems and recommended solutions:
50cc and 150cc units:
Slow idle/poor response when warm: Adjust idle airscrew in ¼ turn increments until idle
smoothes out, and smooth transition to open throttle is achieved.
Fast idle: Loosen idle stop screw until idling at appropriate rate. Adjust idle air mixture
screw until smooth, even idle is achieved.
Quick Method for Resetting Unit Idle:
Set idle air mixture screw to factory baseline setting.
Run unit until normal operating temperature is reached.
Adjust idle to appropriate baseline speed using a tach/dwell meter.
Adjust idle air mixture screw until highest idle rpm is reached.
Turn air mixture screw in or out until idle drops 50 to 100 rpm.
Adjust idle stop screw to baseline idle.
Excessive carbon build up on plug/excessive smoke at idle on two stroke units: Quick
test procedure:
Remove vacuum line to fuel valve when idling.
1) If idle goes up, mixture is too rich.
2) If idle drops and unit stalls, mixture is too lean.
3) If unit runs rough, but continues to idle, mixture is correct.
4) No change in idle noted.
For issue #1: Set idle airscrew to factory baseline setting. Lower idle stop screw until
unit is idling at appropriate rate. Adjust air mixture screw to smooth idle. Repeat
vacuum test as outlined above.
For issue #2: Open the air mixture screw to achieve smooth idle. Idle stop screw should
be left alone.
For issue #4: Idle stop screw is adjusted to far open, or there is a vacuum leak after the
carb slide. Quick test for a vacuum leak is to spray WD40 around the intake on the mist
setting. If the idle changes when this is done, there is an intake leak. If the idle remains
steady, adjust as outlined for issue #1.
No start/Hard start: Same adjustment process as #1, but may have to start the unit with
the throttle partially open until idle stop screw can be set close to the final setting.
