Spark plugs

[jerry101]

i have a 7.5 hsp mercury 1983

i have a 7.5 hsp mercury 1983 model ser #6241553 can anybody tell me what number spark plug it takes and setting also what the compression should be ?

 

[budgie14]

"Hi Gerald,champion says L77JC

"Hi Gerald,champion says L77JC4,1mm gap.NGK says B9HS-10,1mm gap.My 18hp 1984 gets 140 psi,cold,wide open throttle,if thats any help"

 

[jerry101]

"thanks so much ian...could yo

"thanks so much ian...could you tell me what 1mm would be in thousands, and how much compression this motor should have..........thanks again jerry d"

 

[budgie14]

"hi,1mm is roughly .040 thou.i

"hi,1mm is roughly .040 thou.i dont know the correct compression,but any thing over 120psi is not bad.also depends whether its done hot or cold.like i said,my 18hp gets 140psi cold,my 8hp johnson with decompression holes,gets 120psi,cold.my worn 25hp even got 120psi.hope thats some help"

 

[outboard_doctor]

Most outboard manufacturers do

Most outboard manufacturers dont give comp figs...however they do state that all compressions should be within 10% of each other.