Started motors first time this year and starboard motor won't idle in gear. Sputters and gags. Motor runs but drops out for an instant here and there while underway. Tach bottoms out when engine cuts out. Any way tach causes this ? Gaffrig tach 10 years old. I remove batteries every winter and it seems logical I maybe missed a ground wire or similar.

Motors ran fine when I pulled batteries out last October.

Any ideas at all ? Help !

Unfortunately I can't spray anything in the flame arrestor while underway. It doesn't sputter and quit, it's like the ignition is turned off for a millisecond.

I highly doubt its the tach. My guess is VST system is partially clogged.

Plugs, wires, cap, rotor, fuel filters all recently done? Timing checked? Last IAC motor replacement? Fuel pickup in tank clear? Any ball valves or 90's in the fuel lines clear? Coolant temp. sensor checked? Swap coils then ignition module then map side to side to see if the problem switches sides. If all this checks out see VST per Griff. Can you tell I've been chasing an idle issue as well?