johnson AD 10 M ser. 1452476 year and decarb ?

[alittledinghy]

Hi Folks, I am working on the above described motor and it keeps fouling out the lower plug. what year is this motor ? The plugs my BIL installed are Autolite #303. They are supposed to be the modern equiv of what were originally used. True or false ? Would there be a better plug choice ? The motor is really caked with carbon and i will decarb with seafoam if somebody reminds me how. How do i adjust the carb on this motor ? I have a strong spark on both new plugs but i'm unable to do a compresion test as my tester is not with me on this trip. any and all ideas are welcome. Please advise the correct gas oil mixture .Thanks

 

[Paul Moir]

Re: johnson AD 10 M ser. 1452476 year and decarb ?

Dinghy - <br />Johnson AD-10<br />Year: 1956<br />HP: 7.5<br />WOT RPMS: 4000<br />Displacement: 12.4 cu.in. = 203.2 ccm<br />Cylinders: 2<br />Weight: 56 lbs. = 25.4 Kg<br />Gear Ratio: 15:26<br />Spark plugs: Champion J6C (were originally J6J) gapped at .030". The autolites are alright, but you'll likely find the Champions better.<br />Fuel/Oil ratio: 24:1 87 octane gas to TCW-3 outboard oil. Do not use SAE 30W. Stick to this mix.<br /> Picture<br />From the Old OMC Site <br /><br />Never ever rev that engine in neutral, by the way. It's a good engine, but if seriously abused they're known to show their dissatisfaction by letting you see one of the connecting rods.<br /><br />Check out the FAQ forum for Decarb info.<br /><br />Can both sparks jump 3/8"? Strong or otherwise?<br /><br />Follow Joe reeves post to set up your carb:<br /> Carb setting thread

 

[ntoracn@yahoo.com]

Re: johnson AD 10 M ser. 1452476 year and decarb ?

Chech your thermostat. I fixed my 9.9 fouling the bottom plug by replacing the thermostat that was stuck open.

 

[Chinewalker]

Re: johnson AD 10 M ser. 1452476 year and decarb ?

No thermostat on the old 7.5s. Check the coils for cracks, etc. Very common on original issue coils from that era. They may work for awhile, but they WILL let go eventually. New ones are cheap and readily available at Johnrude dealers, NAPA, West Marine, iBoats, etc.... Check points for proper gap and clean surfaces. Heavy pittingmay indicate bad condensers - also cheap and readily available.<br /> That motor MUST be run on a steady diet of 24:1 (or richer, but certainly not leaner) mixed fuel. Because of the rich oil mixed in, they do tend to carbon up over time and decarboning is the way to go...<br />- Scott<br />- Scott