1957 Sea King 12

[Bart]

I have an old Sea King 12 hp that I picked up for 50 bucks a little while back. I put a new impeller, points, and gear lube. No sign of water in the lower unit but I will probably replace all of the seals this winter. I cleaned the carb and everything looks good except for the float. It works but looks like some really rough cork dipped in some kind of coating. I have not had it out on the water, just ran in a barrel. It runs great at higher rpms but I can not get it to idle more than a couple seconds. It then just sneezes a couple times and dies. I tried adjusting the idle control but does not seem to make much difference. I checked for vacuum leaks around the carb with some cleaner and it seems good. It has fresh gas with 24:1 mix. Could the float be causing this? I have it set at the right height and it is not absorbing any fuel. I know it is similar to the Evinrude/Johnson 15 and 18 hp engines of the same era but not sure about the carb parts.

 

[Pappy]

Ignition: If you purchased anything but OEM coils you may have issues supplying spark at a low RPM.
You can remove the flywheel and an aftermarket coil. Place the coil in the running position against the outer radius of a flywheel magnet. Look at the center coil laminate and note the excessive air gap. This excessive air gap can and will affect low speed running quality. The OEM coils have properly ground laminates and will have a very tight air gap and perform as designed.
Carburetion: You need to purchase an OEM kit for this engine. I believe it will be the same kit as the 10hp Johnson or Evinrude. The reason I say OEM is because the kit will be complete with new needle and seat and float assy. The OEM kits are the only complete kit on the market.
The idle circuit on that carb is fed through cast passages sealed with lead or brass shot. The top core plug should be removed during the kit replacement as should the idle needle and HS (high speed) needle. All of the old packing should be carefully scraped out of the needle threads.
Verify low speed fuel flow by spraying carb cleaner up through the cast passages and verifying flow through to the calibration pocket via the core plug opening you made when you removed the core plug.
You should see new carb needle packings as well as nylon washers. Use the nylon washers as bearing surfaces with the packings in between them.
Initial setting of the idle needle should be around 1.5 turns from a lightly seated position. You can then adjust clockwise until the engine runs as designed.
HS needle adjustment can be around 1 to 1.5 turns and adjusted inward until the engine runs at peak RPM then backed off 1/8 - 1/4 turn for safety.
Continue running at a 24:1 mixture. Never run leaner.
Gearcase: The most common seal to leak is the shift rod seal. Hardest to get to but pretty easy to remove and replace. OEM is your friend when purchasing seals.

 

[Bart]

Ignition: If you purchased anything but OEM coils you may have issues supplying spark at a low RPM.
You can remove the flywheel and an aftermarket coil. Place the coil in the running position against the outer radius of a flywheel magnet. Look at the center coil laminate and note the excessive air gap. This excessive air gap can and will affect low speed running quality. The OEM coils have properly ground laminates and will have a very tight air gap and perform as designed.
Carburetion: You need to purchase an OEM kit for this engine. I believe it will be the same kit as the 10hp Johnson or Evinrude. The reason I say OEM is because the kit will be complete with new needle and seat and float assy. The OEM kits are the only complete kit on the market.
The idle circuit on that carb is fed through cast passages sealed with lead or brass shot. The top core plug should be removed during the kit replacement as should the idle needle and HS (high speed) needle. All of the old packing should be carefully scraped out of the needle threads.
Verify low speed fuel flow by spraying carb cleaner up through the cast passages and verifying flow through to the calibration pocket via the core plug opening you made when you removed the core plug.
You should see new carb needle packings as well as nylon washers. Use the nylon washers as bearing surfaces with the packings in between them.
Initial setting of the idle needle should be around 1.5 turns from a lightly seated position. You can then adjust clockwise until the engine runs as designed.
HS needle adjustment can be around 1 to 1.5 turns and adjusted inward until the engine runs at peak RPM then backed off 1/8 - 1/4 turn for safety.
Continue running at a 24:1 mixture. Never run leaner.
Gearcase: The most common seal to leak is the shift rod seal. Hardest to get to but pretty easy to remove and replace. OEM is your friend when purchasing seals.

Thanks for the quick reply. I replaced the points but not the coils. They look like they have been replaced at some time. I will start with the carb kit. Good to know about it being similar to the E/J 10 hp. I kinda thought it was a detuned version of the 15/18.

 

[Pappy]

Just an educated guess on my part. Look in Marine Engine or phone a dealer to make sure. May very well be the 18hp kit.
I stand corrected. Looks like the 54 through 56 15hp kit is the one to use. Do some homework and see if you agree.

 

[Bart]

Just an educated guess on my part. Look in Marine Engine or phone a dealer to make sure. May very well be the 18hp kit.
I stand corrected. Looks like the 54 through 56 15hp kit is the one to use. Do some homework and see if you agree.

Apparently doesn't matter. They all take the same carb kit based on what I'm finding.