I have a capri 26 1991 with a Universal M 2-12 engine that began to run funny last week end. On neutral, it runs great , as soon as i put it in gear, at 1000 - 1200 rpm. it begins to run up and down, from 1000 to 1500 rpm. and shaking around.We' ve been motoring 35 hrs. in the last week and no problem.If I increase the speed, it is less obvious but still there. I have a new shaft. balanced prop but I'm not shure about the alignment. could this have something to do with it cause over 2000 rpm I can feel vibrations that will increase with the speed.Could the misalignment effect the engine running smothly. The day before it all began I poured some Racor product to avoid the growth in the fuel tank like I always does . Could this hurt?