the motor rev sticking is b/c its going lean. not a correct a/f ratio. and i have had to weld a nut like that on a zilla. and it was a major PITA to get it off. a cut off wheel and and some patience. i than used a rethreading set that has thread files and cut the threads back in the crank snout to get the nut off. than had to get the crank rebuilt.