The flywheel adds inertia to the spinning prop what this means is that spikes/changes in RPM's will be dampened, and will let your engine speed spin up a little faster without the extra weight. I don't know how much the thing weighs, so if you take it off you want to re-check your CG.

You can try an 11x6 prop for a sporty trainer prop. You can experiment with different sizes too, but 11x6 is a safe place to start. You will need a new spinner because the 3 holes on your spinner are at 120 degrees apart, not 180 degrees. I just looked at your manual, it doesn't say anything about recommended prop range. Since people are saying that it's not the most powerful of engines, you probably don't want to go more than a 12x5 or 12x6. But play with the 11x6, 11x7, or even 11x5 first.

There are other 3 bladed props, too, but they're more expensive and there are less options.

The needle restrictors are there for someone who has no experience tuning an engine. If you let someone show you how to make adjustments and don't do anything drastic, there is no need for them. Apparently they often are not even set right for optimum performance.

If you make all these changes I think you will be surprised at the difference.