spark-plugs

[henning_dt85]

I need spark-plugs for my engines, i use NGK,what is the right type/heat?<br /><br />1. Johnson 10hp 1960<br />2. Johnson 18hp 1963<br />3. Johnson 9,5hp 1973<br />4. Johnson 20hp 1970

 

[bubbakat]

Re: spark-plugs

1. Johnson 10hp 1960 J4C GAP AT 30<br />2. Johnson 18hp 1963 J4C GAP AT 30<br />3. Johnson 9,5hp 1973 J4C GAP AT 30 4. Johnson 20hp 1970 J4C GAP AT 30 <br /> use champion plugs

 

[alumistar]

Re: spark-plugs

if you want a little more burning power, try <br />J5C, J6C, J7C, or (if your above 4000 feet)J8C.<br />the higher the number, the hotter the spark..<br />p.s.- don't even try a J8C UNLESS your are higher than 4000ft. or you'll melt everything in the head.

 

[talitje]

Re: spark-plugs

for the 18 h.p the N.G.K wil be B7S gapped at 0,30in champion that wil be j4c

 

[rickdb1boat]

Re: spark-plugs

Use Champion plugs(If Possible) in all your OMC engines. They perform better!! Probably tough to get them where your at...

 

[henning_dt85]

Re: spark-plugs

actually the 18hp has B7HS sparkplug, Is that right ( the head is higher so it gives less compression? the only differens on 18hp and 20hp??) Should i use B6s on my 9,5hp (my grandfather always runned it at B6S, and it did not overheat, and one i bought last year didnt overheat. The third I havent runned). Last summer I used the 20hp and it was a bit overheated, runned it with B6S, to warm?<br />I also agreed that the Campionplug is better for these engines, but no body sells them in Norway!!

 

[Paul Moir]

Re: spark-plugs

The choice depends on what the spark plug looks like after you've been running. If the porcelin insulator is dark or black, use a hotter plug. B7S is equivalant to a J4C, and the B6S is a little hotter, like a J6C. The hotter plug may give you a better idle, but make sure it doesn't get too hot when running wide open. If the plug is too hot, it will be dry and powdery.<br />Ideally you want a tan colour. To test, run wide open for a minute, and then immediatly kill your engine. Then remove the spark plug and look at the insulator.<br /><br />The difference between a B7S and a B7HS is the HS has a slightly longer threaded section (.462" vs .375"), so the spark plug is stuck further into the engine. I've seen people run them before, so I guess usually the piston doesn't hit them.<br />For some reason, B6S and B7HS seem to be really popular plugs. B7S plugs are really hard to find.<br /><br />Your spark plugs have little to do with overheating or measured compression. If they're too cold, they will foul at low speeds causing a misfire. If they're too hot, you get knocking and piston damage.