I don't have one of these, but you may be falling victim to long service period interval issues. When was the last service performed. Do a proper period service to be satisfied all the regular service requirements, checks and adjustments are done and go from there......got a manual yet?
The most common possibilities are worn/out of adjust cam chain mechanism, valve clearances, spark timing/advancer operation and adjustment, poor quality/low octane fuel, fuel delivery, failing electrics etc.
Give us some history of use and maintenance and what you believe to be in a good or bad state, and why. Some here may then be able to help better.....
;)otherwise seek out a kwaka site where-in may lie much better direct experience...good luck...