Hi Alan.
I have been ruining petrol engine OMRA boats for just over 2 years now. I am NO expert but i was always told but people who know the folowing.
Screw both the high & low needles fully in. Then take them both out 1 1/2 turns. The needle nearest the air intake is high end and the other low end. They are marked with a H & L. This is where to start from. The engine should run. The Idle screw, take it out and don't use it. Set up your servo to fully close /stop your engine.
Now then when you get the engine to start you may well find if you close / open the High needle 1/4 turn it will rev very well. However this is where every engine set up is a different. Thats the bit you need to adjust till you get it right. The low end needle may also need closing a tad.
I did have on one of my boats a pump set up. the pick up was in the black carb isolation block into the main air way. It has been said if you are not using a clucth then there is no need to fit a pump as the water pick ups will supply all the cooling water you need.
Did you get the engine from new? If so the crank casein gasget should be fine and it is just down to carb settings.
Taking a look at your photos. You need some place for air to get into the boat. Engine need Air to make them work. You seem to have 2 water pick ups on your rudders pipe one to the c/head and the other to the ex pipe cooler bits. One more thing. Disconnect the stop swicth/red button. It will fail when it fills with water and the engine will not start. Its all done by the servo.
Anyway Best of luck