For the price of an engine i would try a couple more things before yng a new one.

First are you sure the servos is not keeping it shut. try unhooking it from the servos, any luck there?

there is also a possiblity that the motor is gummed up with castor oil. im sure someone will ringing in on the proper way to clean the whole engine but i have been told that if you can poor some FRESH fuel onto the crab (so it can sit/soak) there it would help losen the carb up. but this also leads to the qusetion, if the carb is stuck shut was does the inside look like?

Id think some will definitly chim in unteell then you cantry placing a fue drops of glow fuel in the carb and let it sit there