Hello everyone, helping my buddy to fix a 1964 28 hp johnson. Gonna come clean right away, I am not a mechanic or a boating guru. I do most repairs on my car and other motorized stuff by myself however. Including replacing crankshaft on my 1996 seafood speedster. But I am all he's got and I gotta help him. Here's the problem. He bought the boat last year and had one test ride. Says everything was fine. This summer he dropped it in the lake and got a what he described as a gear popping out problem. Towed the boat to my house and insisted that we check lower unit. We opened the lower unit and it was full of water. Replaced all the seals and gaskets, pressure tested the unit and replaced the oil. Got it back into the lake. This is where I rode it for the first time. Engine starts fine idles ok and revs ok. But under load it was jolting every few seconds like it would hit a rock with the prop. Did that at full range of RPM above absolute idle. We pulled the carb off, cleaned it and replaced all gaskets, problem still there. Replaced top crank seal and while did that cleaned and reset the breaker points to .020 inch. I didn't measure the gap before we removed the armature plate but after we installed it back the gap was more like .015 inch. Also tightened all the bolts on crank case. We had new spark plugs put in earlier this summer and old ones were still fine. Tried it again yesterday and the problem is still there. The only difference is that it's doing it every 30 seconds to a minute instead of 5 to 10 seconds. Now, I don't know if the improvement is due to something we did to carburetor, ignition or fixing vacuum leaks and I don't know if we should go after lower crank seal or problem is elsewhere. Need help.
