Oh yeah, I almost forgot. Do make sure that the spark plug cap is really on the the spark plug good. It actually is a twist lock affair. Usually once you get it on a locked, you have a hard time getting it off. But having the spark plug cap on loose is bad as it stresses the ignition coil and can damage it with excessive voltage levels. One thing to never do is see hoe long of a spark one can get off the coil, that typically destroys the ignition coil. The coil can die a slow death like that too. The ignition coil is built into the CDI module.

The other thing is the battery used to power it all with. If the battery can't provide enough current, it can cause the engine to run poorly too.

Also try another spark plug. It is possible to get a bad plug. It doesn't matter what brand either.

Then the timing sensor could be mis-adjusted. The sensor could be off thus causing the engine to not run well. That also leads into some cases where the sensor itself had problems and was defective too.