Re: dead plugs
Maybe we both have weak ignitions. This year I did a few repairs on my 1975 9.9HP (pretty much the same motor as yours). I changed the cylinder head and decided to clean the carb and since I finally located the infamous Champ. UL81Cs I decided to use them as well.
My engine fired up but idled a little rough. The worst part was that it would hesitate badly when I gave it throttle and then lunge out and then bog down and lunge and then eventually my WOT would give me about a troll. It seamed like I had an intermittant spark or fuel restriction.
I did a lot of things including a spark test to confirm my system would jump a 3/8" gap. Anyway, I eventually got around to changing the plugs to NGK B7HS and presto, my problem was gone.
My later thoughts were that perhaps I wasn't torquing them enough. I generally just snug up the plugs and then give them another quarter turn. When checking with a torque wrench to the manual's spec. it is closer to 1/3rd more turn. I don't know if this would make the difference but I just assumed that the NGKs seal up better and since they worked great, decided to leave the NGKs in. I have another motor that uses Champions (J6C) and they work fine, so it may just be an isolated issue with our motors and those UL81Cs.
Good luck.
