Hi, Kai and the usual suspects are:
1. Spark plugs in bad condition or partially fouled.
2. Spark plug cables in bad condition and leaking.
3. Spark plug gap too close or too wide.
4. Faulty ignition coil, module, and or sensor.
5. Battery nearly discharged.
6. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
7. Intake air leak.
8. Water, dirt, or rust in the fuel system, carburetor and/or filter.
9. Fuel tank vent system plugged or carburetor vent line closed off.
10. Carburetor controls misadjusted.
11. Damaged carburetor.
12. Loose, dirty, or corroded ignition module connector at crankcase.
13. Faulty MAP, CKP, O2, and/or CMP sensors.
14. Incorrect valve timing.
15. Weak or broken valve springs.
16. Damaged intake or exhaust valve.
For more information about your issue, please visit the websites below. Good luck and have nice a day.
Owner Handbooks Workshop Manuals Wiring Diagrams for RS1 RS2 RS3 NKD...
Rieju service manuals page 1