Logo
FULL SITE MENU

1972 Merc.80hp 800 sparkplug choice???

fixitdaily

fixitdaily

Regular Contributor
I know I will probably get bunch of different opinions on these plugs but your expertise is always welcomed.I am currently using NGK BUHW plugs but would like to get a new set due to renewing electrical componets(also still have a slight misfire).So my options are:

NGK BUHW
Champion L76V
Champion QL76V
progress.gif
 
Re: 1972 Merc.800 sparkplug choice???

Steve, besides what you have listed up there, Merc also recommended AC's V40FFM's.

The motor would have originally came with L19V Champions. So the L (or QL) 76's would be the modern replacement.

Before the QL76's hit the market, Merc recommended the QL78V's if you wanted the "supression" (Q).

So why am I babbling? :)

All those plugs are "surface gap" which are designed for sustained "high speed" operations (over 4000 rpms) - not always the best all round plug depending on how you use the motor.

So, if you want to experiment (only the cost of a few sparkplugs), a gapped equivalent of the QL78V's is Champions QL77JC4's gapped at .035-.040".

I was running QL78V's and found the JC4's gave (me) better performance for the way I run that particular motor - so something to maybe consider or try out - the regular L77JC4's are only a couple bucks a piece if you just want to "try" before chucking the extra bucks for resistor plugs.

For those of you looking on and saying "this is a Merc so it should run NGK's" - that is true for all Merc Thunderbolt 3 and 4 ignitions - this model has a different ignition system that was designed to run on Champion plugs.
 
Re: 1972 Merc.800 sparkplug choice???

Thanks for the info,as for my Ignition system I do have the thunderbolt 3 ingnition system.Maybe I read into this wrong were you refering that mine doesnt have the thunderbolt 3 and 4 system?
 
Re: 1972 Merc.800 sparkplug choice???

Steve, my parts lists shows a 1972/800 as a 4 cylinder with cap/rotor - do you have a switchbox?
 
Re: 1972 Merc.800 sparkplug choice???

Ok, the first 80 horse models I have listed with a switch box are the 1978 models (with the 80 horse discontinued between 1973 thru 77) - and that's the Merc parts list.

Must be a "glitch" :)
 
Re: 1972 Merc.800 sparkplug choice???

Must be a glitch with the parts list,I have went over and over this to make sure I am dealing with what is exactly supposed to be on my inline 4 , when I got this motor nothing matched from the get go. So to my understanding 1971/72 Merc. used the 332-2986A? switchbox for all inlines until mid to late 70's with the pointless distributor CD Ignition.After that Merc. went with the under the flywhell trigger, multiple coils and a different style switchbox which I have no Idea.Beware,Beware I will get this thing running right if it's the last thing I do.:):):):)
 
Back
Top