Re: What is the recomended spark plugs?
Rather curiously 1977 115 hp does not appear in the plug application list we all refer to! .. at least I cannot see it!
Originals were Champion L77J4 ( or AC M40FFX ) or for sustained high speed use surface gapped Champion UL77V
It is a certain bet is that the modern equivalent of L77J4 ie QL77JC4 would be the current recommendation and that they would be gapped at 0.030" ( rather than the original 0.040")
I would not like to speculate what alternatives to the QL77JC4 would be listed. QL82C almost certainly, possibly UL77V or L16V Surface Gap.
Your model number by the way is 115793 S
