RE: Startup Questions, Gas CAT
B. H. Hanson used to sell these boats RTR for around $1,495.00 but the engine could be one of his.
The plug can be ordered or they might have them in stock at a NAPA store. Auto Zone's or Advance Auto can get them too but they want more for them.
You could have a bad diaphragm. Take off the flat cover off the carb to see if it's wrinkled or damaged. It could be gunked up from storage.
There is radio box tape, generally 3M that hobby shops can get for you through Tower under the AquaCraft/Grimracer name.
The boat appears to be very clean so it doesn't have hardly any time on it.