Re: 6hp Johnson fires good in 1 plug
i just went through that deal with my new to me '74 9.9hp (10rl74s). mine would stop when i pulled either plug sometimes and sometimes one vs the other etc. actually started right up and ran reasonably well on the muffs but only half throttle on the dinghy under load. anyway, pulled the flywheel, found the points somewhat dirty and slightly undergapped. cleaned them, regapped to .02". tdc, set pointer and required gaps all engraved on the housing...very cool. the rest of the business under there actually was surprisingly pristine...good wires, contacts etc. by the way, compression was 85/90 cold as best as i could measure. still runs strong and clean, now.
this motor came to me with branny new champion L82C plugs at .03". this is where it gets interesting since i had the same symptoms after the points routine. i noodled around on the internet and find in some forum or another that the Johnson/evinrude '74-'76 9.9/15 series were notorious for weak sparks and that some guys had figured out that changing to the NGK B7HS plugs at .03" cured their ills. so for $5 and a trip to autozone i stick the ngk's in the monster, fired her up and raced off at full throttle and power for half an hour with a big smile and a fresh cigar. no problemo. time will tell and i am suspicious that swapping new plugs for new plugs can make that much difference but it helped to fix mine just fine.
if i still found no joy i was going to replace both coils which come with all the wires including new plug wires bonded to the coils. i am not sure why the 1974 rocket scientists did not allow for replacing plug wires alone rather than the whole shebang, or maybe i am missing something, but the expense was not too bad for the parts and it looked pretty simple.
as for working on the older engine, i found it a pleasure relative to the newer plastic fantastics and i get a big kick out of ripping around in my inflatable boat with a 36 year old sea horse. i get lots of comments.
sorry for lengthy comments. red sox just beat la 7-5.
