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1986 Mariner 75 hp spark plug

D

Deano27

Contributing Member
I have been looking to see what spark plug to use for my 1986 Mariner 75 hp 4 cylinder. I found that the number for NGK is BUHW-2 which it currently has installed. This is a surface gap spark plug. I have been doing some looking and some are saying that surface gap is better for long WOT runs and the "J" type are better for slower speeds. I run alot of shallow water so I am usually running fairly slow. Can i use a J type plug without clearance issues in this engine? Or do i stick to the surface gap plug? Thanks!
 
Either will work just fine. I prefer the gapless for normal running, the other for jetting (since you can't read gapless plugs).

Jeff
 
Ahh yes I know what you are saying now! Thank you.

One other thing, Should I run a synthetic in my lower unit or will penzoil marine 80 90 work? The previous owner had a brand new lower unit installed and didint run it much but I had it out quite a few times and it shifted awesome but I wanted to change it before the cold winter here in iowa. There was no water and oil looked good but it smelled like fricition modifier and it was greenish blue. Smells and looks diifernt than the penz marine I put in.

Thanks again!!
 
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