What ignition are you running? Most EI conversions will act like that if you have low voltage (less than 9.5v) at the coil.
I had 7.5 at the coil due to corrosion induced resistance at multiple points. This caused my Pertronix Ignitor II to act fine on the fake lake, but fell completely flat in the water and couldn't get out of the hole.
Good luck, look great!