1978 55 HP Johnson - Hole in crankcase, can JB Weld be used?

Hi all,
First time poster, long time reader.

I have a 1978 55 HP (55E78S) Johnson Outboard. It has a new water pump (last fall), new starter, new plugs, new ignition, new battery, new tank, and new fuel line. It ran a couple times this year already, but it was tricky to keep running at idle. Finally, it decided not to stay running. It would start up, (had to keep the choke on), and as the choke would turn off, it would start to rev up (RPM's increasing), and once choke was fully off, it would then die.

So I got a couple carb rebuild kits, did a rebuild of the carbs, cleaning all orifices, and assemblies. Used Berryman's Chem-Dip and then some carb cleaner spray, and blew all holes out (air compressor). The carbs and its parts are spotless. We re-assembled the carbs to spec, verified all linkages were properly setup and sync'ed (per OEM service manual) and then got the same results - it would die once the choke was fully off.

I started to inspect other items, like the fuel pump (to ensure it was getting enough gas, which it is), and I found a hole in the crankcase (see attached pic). How could a hole like this occur? Anyway, can this hole be covered using JB Weld? Or is there any other way to fix this?

I am assuming this hole is the problem: Creating extra air coming into the engine once the choke is fully off, thus causing it to die. This would explain why it sounds so loud too.

Thanks in advance. This forum has been super helpful.

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Re: 1978 55 HP Johnson - Hole in crankcase, can JB Weld be used?

That hole appears to be a thin casting flaw hole. I cant see any indication that it was caused by some flying object, externally or internally.

You can try JB weld for aluminum, but make sure to buff the paint off at least 1/4" around the hole, and clean with acetone before you make a patch.

To be done right, the power head would have to be removed, and TIG Welded by a pro. Hope JB works for you

Re: 1978 55 HP Johnson - Hole in crankcase, can JB Weld be used?

Be very cautious. That motor may be ready to fly apart and make a BIG hole. The connecting rod is hitting the inside of the case. That can't happen unless something is loose. Something is about to bust in a big way.

Re: 1978 55 HP Johnson - Hole in crankcase, can JB Weld be used?

Agree with FR ,the connecting rod must have punched something,yes,that would effect running,have you done a compression test?the reeds ,which control fuel ,work by pressure from in the crankcase.I suggest you take the head off and do a visual ,also check for play on the connecting rod,apply pressure on top of the piston when it begins to return down,and also as it comes up,if you run it and it blows bigtime,there is no rebuilding it for a realistic price.rebuilding that eng.is easy.Have the hole WELDED,no J B WELD