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Older Johnson 2 cycle overheating

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ARL683JA

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I was recently given an older Sailmaster 4 (I think about a 1974) that's not been used much. Cylinder head is a bit brown, I think from overheating. I put a new fuel pump and rebuilt the carb, and it started right up. However, it didn't run long before I could feel the heat. I've since taken it apart a couple more times and made sure everything was lined up OK, but it still runs too hot. Today when I took it apart again, I tried to blow through the tube that goes into the water pump, and no air moves at all. Should it? I can't find a thermostat on this, so maybe it's plugged up. If it is clogged, is there an easier way to get it unclogged? Thanks
 
These engines notoriously run hotter than others, There is no real circulating water jacket on the exhaust side, so it is common for the cylinder head and exhaust plate to be off color, there is an improved design head gasket with larger water passage holes to help with cooling. Impellers are cheap so put one in it while you have it apart. These engines are variants of the 1950's and 60's 3, 3.5 and 4 hp and are wonderful little engines. I can tell you that the cylinder heads run about 150-160 degrees and the exhaust plate can push 175, which is way hotter than you can stand touching with your fingers. I've laser temp measured a number of these engines so the temps are accurate. That said, they do have small water passages that can get plugged from salt and silt. That may need inspection. If a new waterpump impeller doesn't seem to help, pull the cylinder head and check for blockage in the water passages surrounding the cylinder liners and clean it out make sure to keep debris out of the cylinders. These engines are pretty inexpensive to repair and are engineered so well, they are worth fixing and keeping.
 
Interesting reply - I'll have to pick up one of the laser temp gun, which is something I've wanted for some time. There is a new impeller, but that doesn't help. I've watched some videos specifically to see how much water blows out the holes, and I'd say there is as close to none on this outboard. I really think it's clogged, but I didn't want to start on a random spot on the motor, so I'll take off the cylinder head tonight. Looks easy enough. I should be able to track this down, but do you know what to torque the bolts down to? Thanks for the reply.
 
It's actually been running on the boat itself. The shaft is too long for the boat, so I'd say water is at least 8" above the impeller.
 
Cylinder head is off, cleaned off all the debris (considerable amount) and blew compressed air through the water tube. I can freely blow through the tube now. Thanks for the guidance. I ordered new cylinder head gasket, so I'll have this together by the weekend.
 
Those older outboards are little TANKS & very much worth fixing & maintaining as you have. Maybe post a couple pics of it. I really enjoy making old stuff new again.
As a habit, I replace the fuel lines & filter on them as soon as I get them. That' motor is nearly 50 years old & that's cool!! A little ol' Dinosaur lol. You take care of it, & it will probably make it another 50 years. It may not be pretty but pictures are always nice.
Cheers n Smooches
 
ARL683JA said:
Cylinder head is off, cleaned off all the debris (considerable amount) and blew compressed air through the water tube. I can freely blow through the tube now. Thanks for the guidance. I ordered new cylinder head gasket, so I'll have this together by the weekend.
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A good practice on these engines is use a surface plate or a piece of glass (something very flat) with a sheet of 220-320 grit sandpaper taped to it and lap the cylinder head flat in a figure 8 pattern until the entire surface cleans up nice and flat. These little cylinder heads do warp from the higher temps so this will make sure there are no leak issues.
 
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