Means the low-speed needle is not set right... I cannot tell you if its too lean or too rich by the description your giving me...
The way I usually set the low speed needle is: Start the engine, and get it to operating temperature... Rev it a few times just atleast 1 second after I hear the 2nd gear shifting. Leave it standing still for 10-15 seconds, then go full throttle. If its too rich, your engine wont cleanly rev up. Another way to check if your engine is too lean (LSN), is do the fuel line pinch test. Pinch the fuel line near the carburator inlet and count how many seconds before you hear the engine rev up... If it revs up in less than a second, its too lean... A good low-speed setting should be 2 seconds without hearing the engine rev up.
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Selling all my MTX4 parts, bodies, radio and everything!