It may well be within your capabilities stuart23! I would take the injectors out, as it is a simple job, and gives such a good idea of how much carbon is accumulating in the barrels. Something simple to check, but a rigmarole to get off in boats, is the sump, which will give you an idea of any dodgey wear from the quantity and quality of any metal particles settled in it, and in old engines, the mesh on the "oil pump sucker tube bit" may need a bit of degunking. Be carefull not to loose any gunk tho as you dont want it sucking into the bearing oil holes.