I have a 1978 mercury 80hp 2 stroke motor ive been trying to get going but cant seem to get past this final issue. For reference, this boat and motor sat up for roughly 13 years. I pull the boat out and had go redo almost every wire in the boat for batteries, trim, and whatever else coming from the plug on the side of the motor. I cleaned the fuel tank out with new gas and allowed it to dry for a few hours. I replaced all fuel lines from the tank to the carbs. Fully rebuilt both carbs and fuel pump (which i ended up by passing with an electric fuel pump later). I also replaced spark plugs, switch box, rectifier, stator, and trigger twice. I took the boat to a mercury mechanic to check timing, compression, and ensure all cylinders were firing and that all checked good. We also adjusted the mixture screws on the carbs 1.5 turns out.
The main issue: motor runs fine when hooked up to a water hose but once you put it in the lake, you can give it about half throttle, maybe 2,000rpm, and it runs fine. Try to give it full throttle and it bogs down and dies instantly. The reason i changed to an electric fuel pump was because there was clearly a fuel delivery issue before as it wouldnt even hardly idle unless i kept pumping the bulb at the fuel tank, even after rebuilding the fuel pump. Since ive bypassed the fuel pump on the block, i noticed there is no suction coming from that fuel pump. Also, there is usually a puddle of fuel sitting in front of the carbs when you pull that front cover off. Im thinking there is a lack of crankcase pressure but not sure. Any and all input would be greatly appreciated.
The main issue: motor runs fine when hooked up to a water hose but once you put it in the lake, you can give it about half throttle, maybe 2,000rpm, and it runs fine. Try to give it full throttle and it bogs down and dies instantly. The reason i changed to an electric fuel pump was because there was clearly a fuel delivery issue before as it wouldnt even hardly idle unless i kept pumping the bulb at the fuel tank, even after rebuilding the fuel pump. Since ive bypassed the fuel pump on the block, i noticed there is no suction coming from that fuel pump. Also, there is usually a puddle of fuel sitting in front of the carbs when you pull that front cover off. Im thinking there is a lack of crankcase pressure but not sure. Any and all input would be greatly appreciated.