Thanks. When it's in gear, it does not reach full RPM, but does just fine in Neutral. At high revs in neutral, it begins to spit out the black stuff, but is fine at normal levels. A bit of smoke in neutral, but not too bad.
The prop does look a little fouled, that could explain why we're not moving well, but does this explain the issue with the unburnt diesel coming out the exhaust and the lack of revs in neutral?