Why use a spark plug that's not recommended?

[jiminmontana]

My owner's manual for a '64 Johnson 90 hp recommends 3 spark plugs. Is there a good reason why the former owner put in plugs that are different?

 

[tashasdaddy]

Re: Why use a spark plug that's not recommended?

he went to the auto parts store, and that is what the salesman gave him. Many stores do not stock Champion Plugs, and the salesperson talks them into using something else.

 

[ezeke]

Re: Why use a spark plug that's not recommended?

Many spark plugs have been superseded by more recent ones.

The following link has most of the current factory recommendations, but check with your authorized BRP/Evinrude dealer to be sure of the most recent changes. http://continuouswave.com/whaler/reference/BRP/SparkPlugChart2008.pdf

The Champion J4J originally used in your motor has been superseded by the J4C and the RJ4C.

 

[jiminmontana]

Re: Why use a spark plug that's not recommended?

That's what it was ezeke. Thanks, bro.

What about the high-tech spark plugs? Any advantages/disadvantages?

Another thought you may know: In later models, how did johnson get 10 more hp out of the same displacement engine -- whereas my '64 is 90 hp?

 

[Mark_VTfisherman]

Re: Why use a spark plug that's not recommended?

...In later models, how did johnson get 10 more hp out of the same displacement engine -- whereas my '64 is 90 hp?

I don't know this as a fact for the two you have mentioned. HOWEVER the differences in HP for boat motors of that vintage were typically done by carburetor size, and occasionally port timing/reed changes:
9.9/15hp, 18/25hp, 30/33/40hp etc. all shared the same block and c.i.

My 2cents.

 

[Fl_Richard]

Re: Why use a spark plug that's not recommended?

I recall something about HP being measured at the prop VS output shaft of the engine.....

 

[Vic.S]

Re: Why use a spark plug that's not recommended?

I recall something about HP being measured at the prop VS output shaft of the engine....

At one time the power output quoted was that produced by the engine then in 1983 it all changed to quoting the power at the prop.

See http://continuouswave.com/whaler/reference/ICOMIA28-83.html for details

 

[Mark_VTfisherman]

Re: Why use a spark plug that's not recommended?

Horsepower at powerhead vs. hp at prop:
Horsepower is less at the prop.
Numbers would have gone down instead of up.

 

[F_R]

Re: Why use a spark plug that's not recommended?

It really didn't take much tweaking to get an extra 2-1/2 horsepower per cylinder. The 100hp has higher compression. I really don't know whether or not the carburetor venturi size was increased too. Might have been.

90hp cylinder heads were part numbers 307711 and 307263.
100hp cylinder heads were part numbers 312936 and 312935

In addition, the 100hp has a totally different lower unit, making for better performance.

 

[bob johnson]

Re: Why use a spark plug that's not recommended?

That's what it was ezeke. Thanks, bro.

What about the high-tech spark plugs? Any advantages/disadvantages?

Another thought you may know: In later models, how did johnson get 10 more hp out of the same displacement engine -- whereas my '64 is 90 hp?

well many times it is the carbuerator..

I have a 90 HP looper and then bought a 115 hp looper of the same style.

i asked the mechanic i know, how can i PROVE the 115 hp is REALLY a 115 and not a 90, BECAUSE it looks like the EXACT same motor...

he said measure the throat of the carb...

I did, the 115 throat was way bigger!!!

the motors are the same bore and stroke( dont know if the porting was different)

bob

 

[ezeke]

Re: Why use a spark plug that's not recommended?

Anyway, what they usually did was to find a way to increase the top RPM and rate the engine at a higher RPM. You would not notice much difference until you entered the high end of the full throttle range.

 

[jiminmontana]

Re: Why use a spark plug that's not recommended?

You guys ROCK!

 

[Texasmark]

Re: Why use a spark plug that's not recommended?

Because you just don't want to. Recommended stuff is just that because the OEM is trying to supply something that the general public will get the most benefit using. Since they (the general public) do all sorts of things with their stuff, the OEM tries to average out all those variables and come up with one solution.....like a "standard" prop on lower hp engines for example.

I run standard gapped plugs in my 2 cycle even though OEM's on "both sides of the aisle" recommend surface gap. Standard plugs work better for me in what I do and I use them whereas surface gaps didn't. They work, they are happy, the engine is very happy, I am happy and what else can you say....let's go fishin.....where's the worms.

Mark