I’m having a big issue, I got an 85 carrera 205 that will run fine on a hose, but as soon and it’s in the water it runs like total shit then not at all. This is with it on the trailer still just backed up far enough that the pump and exhaust are in. The motor was just rebuilt last month as a long block and hasn’t even been broke in, Heres the specs:
454 BBC roller motor w/mild cam
Weiand intake
Quick fuel 750 dp marine carb
DUI marine HEI distributor (timed 10-12 initial, 34-36 total)
Ac delco plugs gapped at 50
Indmar through transom exhaust
High torque mini starter
Rebuild Berkeley 12JG with ride plate and electronic jetovator

There doesn’t seem to be any wires touching the water or anything when I back it in the water on the trailer, it seems to me like the ignition shorts out when in the water somehow, but I’m completely perplexed on how that could be a thing, I thought maybe the starter is shorting internally causing it to somehow short through the block when the exhaust tips or grate are in the water? I can pull it out on the launch ramp, wait a minute or so, then it runs normally, but the second I back into the water ( even when still running) it idles like shit, has no power and eventually just dies then can’t be restarted til I pull it out of the water. If anyone has any ideas or has been through this before please let me know, here are some pics

Sellin my muscle car project
69 mercury montego
351w with fmx trans
Factory front disc brakes need worj
Centerlines with air shocks in rear.
Has some rust and driver fender damage.
Runs, drives, stops, and sounds mean a hell
$3800 firm

'79 Caribbean 1950 18'