Instead of arguing over what your manual states and what my manual states, the proper answer for the original poster will depend on what model he owns. Obviously your owner's manual calls for one type of spark plug and my owner's manual calls for a different one. Neither of us are wrong with regard to what our equipment uses. However, and again, the correct answers depend on what the OP is operating. From the looks of the mower in his picture it's definitely older than my 2000 model.
My main and only real objection was the reference to the Champion series 8 plug, which as I said experience has shown me is not a great match for Lawn Boys.
I can't find exactly how much the tip on the BPM4a projects. NGK only specifies the tip as projected or not, whereas Champion offers about 6 different projection lengths. From reading around a bit, if one wanted a 14 heat projected tip, a CJ14Y would probably be the correct one, but that plug doesn't seem to exist.
Regardless, whether using a projected tip or not, experience with a range of Lawn Boy engines tells me that the really, really hot BP4Ma or CJ-14 leads to easier starting, better/more consistent running, and a plug less likely to foul in these engines. I did just look and I had pulled a CJ8 out of a mower at one point or another that was a cantankerous starter and would lose power or 4-stroke far more easily than I'd have expected. Even cleaning the plug, which I do before replacing(honestly these things seem to last forever, especially if they're the proper temperature plug, and if I do anything to clean I'll wire brush by hand with a brass brush then carb cleaner and finally compressed air) didn't help, and it showed a strong spark out of the mowerr. A CJ14, which is what I had, made a big difference almost immediately, and even more so once I re-adjusted the carb to it.
The OP shows an electric start F engine compliance era mower, probably with the 3 speed transmission. It looks to me a lot like a 10515, which is manual start but with the 3 speed transmission. I don't know the electric start model number off the top of my head(spitballing it may be 10537, as the the manual start 3-speed Duraforce is a 10525 and electric is 10547) which is likely a mid to late 90s mower. The service page I posted above is for the pre-compliance and early compliance F engine. It may still spec a CJ-14, or it may spec the BM4a or BPM4a. If the OP fitted any of those plugs, they're likely to be very happy with the operation.
(at least she tried). Now it smokes really bad and basically died and won't restart. Since she's out town, I'm going to gather up some stuff to get that one and her other mower running again.. What spark plug does it take? Oil ratio? 32 or 40 to 1?What about the air filter? Is it serviceable or a paper type? This is the only picture that shows anything, hopefully someone will recognize the machine.
