Weird issue
 

first off here is my set up...twin 360cu in small blocks with blowers and dual 750s, mechanical fuel pumps, and a complete MSD ignition from boxes to distributors....Now on sunday ran the boat all damn day, started and stopped about 2 dozen times and then it got dark and pulled the boat, it was late soo the flushing would take place in the am...Monday morning I hook up the hose and off i go..so i think turn the water to port motor and hit the key...cranks and cranks give some throttle and nothing...has fuel pressure. i am pretty pissed off but deep breathe and switch to starboard motor and dont you jknow does the same god damn thing...i assume its spark but now i need to go to work......fast foward to 7pm monday for giggles i but the boat on the hose and VROOOOM both motors instantly fire and sound fine. i scratched my head and called my dad he said maybe the MSD is acting stupid, i said gee thanks pop good advice. again fast foward to today figured why not 10:30am hose on boat and both crank but no run.

A little more. Both motors have isolated batteries and electronics

PLEASE HELP

is the boat sitting outside? Could it moisture from dew?

Yes it is outside. Stays covered 98% of the time and the last three days have been almost identical in weather as well. I'm really confused and out of ideas. Have changed coils. MSD boxes. I am at a loss

well seems pretty weird that both would suffer ignition failures at the same time and come back at the same time...do you have a safety lanyard ??? if so I would change that...one of the only things that would take out both..

Each motor has a lanyard

Any more ideas. I really need help

Maybe some kind of grounding issue? Seems weird that both motors fail at the same time due to an obvious elec. issue?

Even though each motor is totally separate ?

They should share a common ground, most have a ground strap linking the engines.

Did you confirm that you have no spark? Have you pulled the dist caps?

Had a friend that could not start his boat in the morning, but it would start later in the day. Pulled the cap and there was green corrosion on all points. I changed the cap and rotor no problems since. My thought was the corrision combined with the moisture that had not burned off from the night before caused the issue.

DSo they both share one fuel tank? Possibly something fouling the fuel pickup?