Johnson 70 (1997) Plug Question ?

[gpsguru]

Been searching and reading about spark plugs on here today ????.. I think I have the answer , but can anybody confirm my understanding.

Jonhson 70 (1997) ????.. I will use the boat for mostly in shore trolling with the occasional trip to about 5 miles out, so I guess I will need QL78YC plugs as they will be better at slow running due to being a hotter plug.

I also have some QL16V surface gap plugs, but I guess these are better if you are mostly going to be WOT as they are a colder plug so may oil when running at idle for long periods?????.

Right or Wrong ?

 

[Vic.S]

Re: Johnson 70 (1997) Plug Question ?

QL78YC are the currently recommended plugs for the engine. ( gapped at 0.030")

 

[v20 outrage]

Re: Johnson 70 (1997) Plug Question ?

The QL78YC is the recommended plug,..."BUT"....the QL77YC works better in my 1997 - 70hp as I troll 4 - 6 hours at a time on mine.
I used 78s for years & my engine started stumbling once in a while when trolling for long periods.
The 78s are great plugs but they do better if your not a big troller.
The person that re-built my engine recommended useing the 77s if I trolled alot & it really helped.
He said the 78s are better if you run at higher rpms than trolling.
Sal

 

[Vic.S]

Re: Johnson 70 (1997) Plug Question ?

The QL78YC is the recommended plug,..."BUT"....the QL77YC works better in my 1997 - 70hp as I troll 4 - 6 hours at a time on mine.
I used 78s for years & my engine started stumbling once in a while when trolling for long periods.
The 78s are great plugs but they do better if your not a big troller.
The person that re-built my engine recommended useing the 77s if I trolled alot & it really helped.
He said the 78s are better if you run at higher rpms than trolling.
Sal

I draw a blank on QL77YC. Maybe obsolete or perhaps you mean QL77JC4. It has a different design tip and ground electrode to the QL78YC and it was one of the plugs originally listed for the engine.
Often QL82YC is listed as an alternative to QL77JC4 . That is a little hotter and is useful when trolling a lot.

 

[seahorse5]

Re: Johnson 70 (1997) Plug Question ?

the QL78YC and the QL82YC plugs are warmer and more foul resistant than the QL77JC4. You can also use the warmer QL82C which is equivalent to the NGK B-7 series plug.

 

[Auxlarry]

Re: Johnson 70 (1997) Plug Question ?

I troll a LOT on my 85 115hp and have used the QL82YC for years and have never fouled a plug. Change them twice a year and and enjoy boating!

 

[v20 outrage]

Re: Johnson 70 (1997) Plug Question ?

typo,...left out the "C" on the 77s
Seahorse5 is the expert on these & most other engines.
Sal