OK, i have tried everything i know to get this motor to run smooth.Unfortunatly i dont know that much. Here is what i did so far. Rebuilt carbs,replaced powerpack and coil,set points,troubleshooted fuel pump per manual and so on. The motor when started up for about 10 seconds runs smooth. After that it starts missing and coughing and it smokes pretty bad.My compresion is about 105 on all cylinders oil is leaking from gear box.I have spark on all cylinders i have a vented gas tank and new gas mixed at 24:1. I dont know what to do next. Ive never had this boat on the water. I am running it in a barrel of water with the shaft approx. 2 feet submerged and the barrel is about 3'x3'. It seems that the engine is running rich and coughing on its own exhaust. Could the way i am running it cause this. Well as you can see im frustrated and about to pitch the engine. If anybody has any advice on where to go from here it would be much appreciated.