1975 850 Type III Ignition Spark Plugs

[1960 Starflite]

Good afternoon, I am bringing a old 850 back to life to install on my pontoon. My Setech manual calls for Champion L76V spark plugs. It has L78V plugs installed and they are sooting looking with an oil film on them. Thinking it was running rich, so am going thru the carbs and then check timing when I get it running.

Question 1: Being on a pontoon, running only WOT on occation, where should I start with spark plug selection?
Question 2: This engine has a 19 pitch prop, which I think is way too much for my 24 ft pontoon, wont reach correct RPM's, Right?

Will be a while till I can install on toon, summer is here and the old 650 (1963) is running good. But will be running the 850 on muffs for now.

Thanks, Tom

 

[Chris1956]

Re: 1975 850 Type III Ignition Spark Plugs

19 pitch prop is likely too much. The difference between L76 and L78 is not much. Some of the old 850 called for L78 some for L76. There is no way to substitute hotter or colder plugs for the surface gap plugs. Also that motor will run kinda rich at idle. it is the nature of the beast.