Just finished putting together my DB30 and I have to say it's well underpowered. Waiting to hear from cjtmini about the parts kit availability before I pull the trigger on a Lifan 6.5hp here locally.
Here's a few things to make the stock DB30 go better until you do the engine swap:
1.) Change the oil.
2.) Pump up the air pressure in the rear tire (20 psi is what most use as rule of thumb).
3.) Drill out the muffler. Two 3/8" holes through the exhaust outlet in the muffler. Be a good idea to remove the muffler first.
4.) Back out (or remove) the throttle stop screw.
5.) Experiment with the choke lever. Some DB30's run better with the choke somewhere between the on and off positions.
6.) Use high test (or "premium") gas.
When you order the 6.5 clone installation kit from cjtmini, be patient for the delivery. I live in Virginia and it took 5 days for the kit to get here from Michigan.
Jimmy S.