Bought a Johnson 84 50HP 2 stroke, which was completely rebuilt 2 years ago. Engine was running fine until this year, top cylinder keeps cutting out after 15mins. run time. Engine starts up fine with both cylinders, runs fine for anywhere between 15-30mins ... then we lose the top cylinder. <br /><br />We take out the spark plugs ... dry them off (top one is wetter than bottom), let it sit for a while, reinstall ... and works fine again.<br /><br />We have replaced the spark plugs already ... as well as the fuel tank (we thought it was a bad fuel valve which might have been providing a poor air fuel mix) ... also cleaned out the top carb and adjusted flow. Still was occuring.<br /><br />Next we checked for spark ... and after charging battery completely had positive spark on both cylinders. After which we tested compression. We have 50 on the top and 75 on the bottom. Although it sounds like we might have a stuck ring, would this cause this kind of problems (we don't see any smoke, and engine starts up fine).<br />We have just added some crankcase cleaner to see if we can unstick the rings.<br /><br />However, would appreciate any other suggestions.
