Just bought my first boat last spring. What started as an intermittent problem has become a full time problem. Motor cranks and idles perfectly. It used to run full throttle perfectly. If I reduced throttle at cruise even a little it would start stuttering and jerking. Now I can't go above 1/3 throttle before it starts and the horn sounds. I installed a new water pump and fuel pump. It's been tricky as there is no serial# tag and the silver medallion on starboard side of motor seems to be from a mercury. There is an M at the top and G2595843. I have it guessed as a 1988 Johnson 20 or 25 hp. I drained the float bowl and it looked like clear water coming out. Any help would be greatly appreciated.