If it's my conversion there is no leaky block and no pressure port in the block...the pressure comes from the fitting in the case under the carb and goes to the carb back plate through the black neoprene tubing...
Most likely cause of the problem is a stiff diaphragm in the carb...Carbs don't leak when everything is right....
Some of my old conversions had ignition problems....Look at the back cover, if there's only 1 nylon screw holding the circuit to the plate you can send me the engine for free replacement of the ignition...It WILL run right when you get it back..[8D]