Spark plug confusion

[Sascwatch]

i picked up a 1987 25hp 2 stroke Merc and it currently has Champion QL77JC4 plugs in it, online parts manuals list the Mercury part number 14103570 which through google searching brings up the NGK 2173 BUZHW-2 surface gap plug. The NGK website lists the BPZ8H-N-10 as the recommended plug, this is a normal type plug. These 2 plugs are the same size but are very different, the first had a heat range of 12, the second is 8. The gaps are different aswell, .071" and .039". Neither of these cross reference the champion plug that is installed.

I've confused myself on which plug to run, motor seems to run fine minus the odd hiccup at idle in cold water. What do you guys recommend? Thanks in advance.

Edit, I'll add that this engine does not have a thermostat.

 

[flyingscott]

I have the same motor run the BPZ8H-N-10. The QL77jc4 plug is an OMC plug, I run them in my Evinrude 70 hp, not a mercury recomended plug. Don't know where you got the gaps from both get gapped at .030. Does it not have a thermostat in it or just no place for one.

 

[Sascwatch]

Awesome, I'll get a set of those tomorrow. Thanks.

 

[Sascwatch]

There was 2 different designs for this motor, one with and one without the thermostat. There may have been a few other changes, but that's the biggest one I see in the parts diagrams.

Gaps I listed were for the 2 NGK plugs off their website.

 

[flyingscott]

Sorry about that the gap is .040 for that plug. Yes there is design 1 and design 2 blocks main difference is the design 2 motor has a thermostat and can be rebuilt.