I would reset the needle on the carb to what the manual says and try that. Replace the glow plug and make sure the heater is charge.
When you set it don't twist the needle back and forth, set it and leave it for a few minutes so the engine has a chance to see the effect.
When you twist the needle , the change does not happen immediately.
Yes a starter box will alleviate a lot of the frustration, you will also still be able to use the pull starter.

I would not suggest taking the engine apart and such at this point as you really have no idea what you are doing.
You will cause more harm than good.

If you think there is an internal problem with the engine, you need to take it to the hobby shop, or if you cant resolve the issue take it to the shop.

Let us know

Dbow