OD type F plugs are mainly for 4-stroke engines so they are hotter since a 4 stroke fires every other rotation of the crank.

As far as fuel delivery, I'm not sure on the Moki, but you may need to put a pump on this one but that depends on something else which I will address at the end of this post. What you did as far as fuel lines works very well for the OS160 but the Moki is even bigger in CC amounts (read that as volume) so you may have no choice. You may have been better off with the standard Slimline instead of the oversize can version. The standard one would have given you more pressure.

You said it in your first post, changing the needles does not change the tuning. If that happens the engine is not getting fuel.

Also, if you have a fueler valve installed (Dubro or Slimline), the type that you plug a probe into to fill the tank, remove it as well as you could be getting air as those are well known to leak and do a three line system with a fuel dot.

I do not believe changing plug is going to do a thing in this case, it's a fuel delivery problem.