gordmac

Seems I might have caused some offence! It was a genuine question, I had a family event in the deep South and on the way down came...

Anything else happening like smoke? Are the revs down as well as speed?

Don't want to cause offence but why would you want a high speed planing Hull in a river?

Take the plugs out before turning it over. This will let oil out of the bores if there is enough to hydraulic it and let you clean any...

Idle jet as above, in olden days jet cleaning involved blocking and unblocking the carb mouth with your palm with the engine running...

You will need some sort of fire ring round the bores.

Copper?

Oil level ok?

Swap the starters over and see if the problem follows?

Might be worth asking on a rib or fishing forum. They tend to have outboard powered boats.