Yanmar 3QM30H YP10 no neutral position

[Ocean Child One]

I am currently in Vuda Marina in Fiji. I have a Yanmar YP10 gearbox. I recently got a mechanic in Hobart (now not much help) to overhaul the gearbox. After re-fitting I noticed there was hardly any "neutral" position, and now there is no neutral position... as I move the gear lever (I have checked the cable by the way, and I am using the recommended oil which is basically just the same as the 15W-40 oil I use in the engine sump) the engine goes straight from forward to reverse with effectively NO neutral position. I have looked at the workshop manual but I can't find anything useful (to me) there. I note there is an adjustment screw, with a lock nut, at the little box where the gear change lever enters. I loosened this slightly (using the 'trial and error' method) but nothing changed. Any advice would be much appreciated.