The problem of having an engine “sputter” is typically caused by a fuel system issue. For pit bikes with smaller cc displacement engines, in order for a cylinder to fire efficiently, three separate components must work together; the fuel delivery system (carburetor), the ignition coil and wires and the spark plug. Typically with most pit bikes, the problem is going to be with the spark plug or the carburetor; with the fuel system being the primary culprit.
The first step we recommend is to check the efficiency of the spark plug. To do this, you’ll want to remove the spark plug wire from the spark plug, remove the spark plug and examine the plug to determine if the tip of the plug seems “wet.” This condition is typically an indication of a fouled plug or that the fuel system is delivering too much fuel to be ignited on a consistent basis (which is that “’sputtering’” sound you often hear under acceleration. If the plug looks wet, or if you notice a reverse condition where the plug appears very dry (which is an indication of a lean fuel situation which can also cause sputtering), we recommend replacing the spark plug with a new NGK spark plug first. The spark plug is a CR6HSA or CR7HSA NGK.
The next thing that you want to check and clean the carburetor. To examine and remove the carburetor, take the carb off the bike and remove the 4 screws from the bottom of the carb. At this point, you’ll see two gold screws. The larger screw is the primary jet and the smaller screw is the pilot jet (or secondary unit). While ensuring you are wearing safety glasses, apply carb cleaner vigorously through the holes of the jets and through the entire carburetor. You should then use compressed air to blow any gunk or debris that could be stuck in the jets or the bottom bowl inside the carburetor.
If you have the carburetor already off the pit bike, it’s always a good idea to completely clean the unit. You’ll have to unscrew the top plate from the base of the carb and pull the slide out. Whenever you pull the slide out, take the needle out of the slide and move the “c” clip on the needle up one slot. Follow the steps above for cleaning all components inside the carburetor and reassemble. Put everything back together and check the performance of your pit bike and the ‘sputtering’ issue. If the issue continues, it’s possible that the carburetor is defective.
Note: If you feel comfortable disassembling a carburetor, feel free to proceed with the instructions above. However, if you don’t feel comfortable, contact our technical team and we can help you through the process or recommend a local mechanic.