I take it its a four stroke 1600cc jobbie?
We had a problem with a mysterious intermittent but serious misfire that was taking two cylinders out.
Luckily we have Jim, a brilliant independent mechanic around here(-plus some cowboys eh!) who thought it must be the cdi unit but then scratched his head, talked to another friend in the trade and came up with the fault being the interupter switch. A considerably cheaper fix.
Located on the port side of the motor under the cowling and hidden by the bottom tray the switch is activated when changing into and out of neutral and drops the motor down to 2 cylinders to relieve pressure on the gears during shifts. Ours was interupting but often forgot to stop interupting when its job was done (sounds familiar eh !
The switch is now disconnected & engine is fine
Our mechanic says these are a familiar bit of kit on big inboards but had never noticed one/had a problem with one on an outboard before
you may just need to disconnect a wire
If not we will give you scrap money for it and I'll leave it with Jim for a coupla days to sort out!