'66 100hp johnson spark plug question

[boostin_7]

Hi,
I've been trying to sort out a miss/stumble at light throttle. Done a link & sync & tuned the carby to what i feel is a pretty good setup.
This has made the power delivery nicer, shifted the stumble lower in the rev range & has seemed to reduce the severity.
Now i want to replace the plugs/points & check the leads & coil.
From what i've read i need to use either champion J4J or J4C or NGK B6S or B7S.
My question is: the plugs in it at the moment are NGK B9HS, is this a good plug to be using or could be causing issues?

 

[Haffiman]

Re: '66 100hp johnson spark plug question

B9(HS) might be a bit on the cold side making idle a problem.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

which plug do you reckon i should try next? The NGK B6S or B7S would be the easiest for me to source because most of the part stores near me only have NGK or Bosch.

 

[Haffiman]

Re: '66 100hp johnson spark plug question

Bosch is not an option!! NGK gets hooter the lower the number, Champion gets hotter the higher the number. The recommendation for your engine I believe has changed to J6C and the NGK equivalent should be B6S, which I would have tried first. If running hard, B7S might be a better choice, you may have to test.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

thanks, I'll give the B6S a shot & see how i go.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

Chucked a set of B6S plugs in today & first thing ive noticed is that they are quite a lot shorter than the B9HS (i.e dont go as close toward the combustion chamber).
Also for some reason my original looking leads really dont like going on these plugs, they wont 'click' on like the others.
The leads are quite hard & brittle looking, so what would be my chance of getting replacements for such an old motor.

 

[Haffiman]

Re: '66 100hp johnson spark plug question

Are you sure about year and model:
http://www.ngk.com/results_fitment.asp?pid=b6s

Scroll down the list and you find the 1966 -100HP.
However if going to 67, the recommendation is Champion L-19V which is a completely different plug type.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

Yeah 100% sure on the model as its a 100hp with the battery ignition style setup (not magneto) which was only made in 1966.
It ran on the plug fine, but i was just worried about the leads now, & when i took the loosest plug off of cylinder 2 it make no difference what so ever to how it was idling.
Next weekend Ill be taking the boat out again, so ill see how they go under load in comparison to the B9HS. The B6S plugs did seam to stay cleaner though after the few mins i ran the engine with the flush attachment today.

 

[Haffiman]

Re: '66 100hp johnson spark plug question

Next question:
Sure you have the corresponding head for a 66 and not heads for a 67??
Reason for question is that normally putting in a B9HS plug in a 66 head, the pistons would smack up the plugs. The J6C plugs have shorter threads than the B9HS. Measure the length of plug threads and compare with the plugs, they should correspond. If you are running 76 heads, plugs to use might be B6HS and not B6S

 

[boostin_7]

Re: '66 100hp johnson spark plug question

hmmm ok sounds like ive got the 67 heads then as the B9HS ran in it no worries.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

Im a little confused now as on the NGK website, the B9HS doesnt list any outboard motors in there application list.
The B6HS does have some outboards listed, but no evinrude/johnson ones.
Do you definitely think the B9HS plugs would be too cold & a lower number in the same range (like the B6HS) would be the correct heat range for my engine?
Also any ideas on where to get new leads?

 

[BonairII]

Re: '66 100hp johnson spark plug question

Why not just get the Champions that Johnson recommends? NAPA def carries them. Order them online if you can't find them locally.

 

[Haffiman]

Re: '66 100hp johnson spark plug question

First of all you have to figure out which heads you have. Should not be such a big problem, as mentioned just count number of threads and compare with the plugs or simply measure.
The 67 calls for a surface gap plug, but your ignition system will not handle the power needed to run them.
If 67 heads, you will need to run 'normal threaded' plugs in the Champion J6C heat range.
First figure out the 'REACH' of your plug!
http://www.championsparkplugs.com/faqmain.asp

http://www.championsparkplugs.com/sparkplug411_manufacturer.asp?manufacturerID=2

 

[boostin_7]

Re: '66 100hp johnson spark plug question

Sorry i miss understood what you wrote before about measuring the thread of the plugs.
Well i just did it & the head has the same number of threads as the shorter B6S plugs, so it looks like the original '66 heads are still on this outboard.
Any ideas on why the longer plugs didnt get munched by the pistons & cause damage?

 

[Haffiman]

Re: '66 100hp johnson spark plug question

I guess you have been lucky?? At least it confirms which plugs are the right ones.

 

[JB]

Re: '66 100hp johnson spark plug question

Why not just get the Champions that Johnson recommends? NAPA def carries them. Order them online if you can't find them locally.

Exactly. All JohnnyRudes are designed to use Champion plugs. This whole thread explains why. J6C gapped at .030" and you can stop trying to outsmart the guys who designed it.

 

[boostin_7]

Re: '66 100hp johnson spark plug question

Ive only had this boat for about 6months & it looks as though its been running the B9HS plug for a while as there was another new set with the boat plus a few sets of used ones in his spares box.
The guy who owned the boat before him was a motorbike mechanic, so maybe thats why these motorbike plus were being used & the following owners just followed suit.
Anyways, in regards to why Im using NGK.....None of the local part shops (supercheap/sprint/repco) ect stock champion plugs & none are interested in trying to get them...
I just fed the usual the NGK equivalent is XXX so here you go.

 

[Haffiman]

Re: '66 100hp johnson spark plug question

I see no problem in substituting Champion with NGK in your case, your ignition system is rather straight forward. Only problem might be to find the right heat range. Usually NKG covers several Champion plugs as it looks like their heat range is 'bigger' than Champion. By experience it looks like in most cases a direct cross from Champion to NGK gives a colder plug, probably out of fear running a too hot plug that is more dangerous. Just test it out and find the best solution for you.