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Older Johnson 40HP smokes like crazy

J

Jon Dinsmore

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" 1962 Johnson, model RDS-24L,

" 1962 Johnson, model RDS-24L, 40HP 2 stroke twin. Starts easily but smokes heavily. There is also a lot of oil in the exhaust. New plugs were installed when I got the engine so I can't tell much from them. I do not recall exactly what gas/oil mix I was using but I am fairly certain it was the recommended ratio. I checked compression and got 60 psi on top but only 30 on the bottom. I am assuming the powerhead needs to be rebuilt. Or is there something else I should be looking at first? If the powerhead does need to be rebuilt could someone recommend a shop experienced with these motors. Thanks - Jon "
 
"Jon.... The fuel/oil mixture

"Jon.... The fuel/oil mixture would be 50/1 (1 pt 50/1 oil to 6 gal gas), 87 octane fuel is okay.

Both of the compression readings you state are low, but a difference of 30lbs between cylinders indicates even further problems.

It (hopefully) might be simply a blown head gasket between the upper and lower cylinder which might allow a bleed over from one cyl to another if it were blown bad. However by the same token, if this were the case, you should be having a problem with water entering the cylinders also.

The spark plugs should be Champion J6C plugs gapped at .030.

If you're absolutely sure of the compression readings, I'd suggest that you remove the cylinder head to inspect the head and block surfaces, head gasket, piston and cylinder walls.

Let us know what you find.

Joe (30+ Years With OMC)"
 
" Jon;In 1962 the fuel/oil rat

" Jon;In 1962 the fuel/oil ratio was 24:1=1QUART of oil to 6 gallons of "white gas" which now is only Amoco hi-test {93 octane}.If you don't have a blown head gasket try using Engine Tuner to free-up the rings,just remember that a 40 year old motor is NOT worth spending very much $ on,make sure the thermostat warms up the engine it should idle at about 140'=+/- Good Luck Zeke "
 
U need to decarb ur engine with seafoam or engine tuner to free ur rings to get more compressor, below 90 is bad, recommended ratio was 25:1 but that was in 1962 when engine oil quality was low, so u have to run 50:1 with ur air/fuel mixture screw settings @ 2 turn anticlockwise from slightly seated
 
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