Spark plugs

[BogMonster]

On my Johnson 2 stroke 115GL:

The recommended spark plugs are Champion QL78YC. I ordered these from Oakleys and they sent QL77JC4, only just found this out when I went to change them and looked up the correct gap etc. to find out the ones I have are slightly different.

Not clear on what the difference is - presumably heat range but anything else i.e. what does the JC4 bit mean?

I've been using the NGK equivalents to the QL78YC for a while (BPR6HS) but it is starting to develop a bit of a misfire when its been idling for a while (or rather it always has that and it is starting to get worse and taking longer to clear - so I figure its time for a new set of plugs). The NGK's aren't proper marine plugs so I figured I would put the "proper" ones in - and now find the ones I have are different (and there is no chance of getting the Champion marine ones here as I've already checked...)

I did a bit of Googling but most of the results which appeared to give info on the comparison between the two came up as "page not found" - what do people think regarding whether it is OK to use the 77's or not? My other option is to get another set of the NGK's which I know work OK as they have been in there for about a year I guess.

I have 3 sets of the QL77's so if they should be OK then I will use them but just thought I would canvass some opinions...

Thanks

Stephen

[BogMonster]

More on this:

Have just found a set of QL78's that came with the boat when I bought it, and the main difference (apart from probably the heat range) is that the centre electrode on the "right" ones protrudes quite a bit further from the end of the plug body - will the more recessed electrode on the QL77 mean that it is more likely to foul when idling, or less likely to foul? I'm guessing more likely but I suppose as I have them I might as well use them if they are OK, and see what happens.

Edited again to add:

Photo attached, on the left one of the NGK's I just removed, in the middle the "right" plug the QL78, and on the right, the QL77JC4.

One of the NGK's was rather wet (lower cylinder port side) which probably explains the misfire at idle, and all of them had much bigger gaps than they should have - about 40 thou (correct gap is 30-32 thou and i know they were right when fitted because I gapped them with the same feeler gauge) - is this sort of electrode wear normal for a set of plugs after about 70-80 hours? Other than the gap and the inevitable slight saltwater corrosion on the outside of the body, the old plugs are in pretty good nick.

[Chris]

Stephen I dont know if this applies to your engine but I know that on my old Johnson 90 V4 60degree looper there was only one sort of plug that should be used and it was the Champion QL78YC other plugs can cause problems.

I am not sure on the age of youre engine but this may not apply however its worth checking.

Speak to Lee at Fairweather Marine hes good on the older engines.

Chris

[BogMonster]

Ta - this engine was fitted out in 2000 but I think may be an older model year - its an OMC engine not one of the new ones. I found a set of new QL78YC plugs that I had forgotten about - came with the boat and now put those in for the moment - but if anybody else has any thoughts on whether it is safe to use the QL77s I'd be interested to know, as I remember they weren't cheap and I don't really want to dump them if they are OK to use!

I shall try and contact Oakleys and see what they say, could just have been a screw up I guess.

[BogMonster]

Hmm just been hunting around and found this

had to use the Google cache as the page was not available:

Posted on Friday, April 21, 2006 - 12:44 pm: Edit Post Delete Post View Post/Check IP
does anyone know the correct plugs for a 1996 150hp johnson ocean runner. the manuel says QL78YC but the motor has QL82YC in it. its a used engine so i don't know which is right. thanks
willard king




The QL78YC is the plug it came out with but I would run QL77JC4 in it and gap them at 40 it will idle better and run smoother.
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HOUTEX




HEY WILLARD,, DIDN'T THEY COME OUT WITH QL77JC4
AND THEN IN 98 SWITCHED TO QL78YC ?? MIGHT WANT TO
DOUBLE CHECK YOUR RECORDS.

I guess the 150 is another version of my 115 (the workshop manual also covers a 150hp version)

What is the logic behind using the JC4 plug and increasing the gap by 30% (specified gap is 30-32 thou, but this guy is saying 40 thou)

I should know this, but what is the effect of using a plug with too big a gap?

thanks

[ian parkes]

if the correct plugs are a protuding elctrode and the others are a flush electrode i would say its a completely different and wrong plug .
Iam not sure what the champion numbers mean but it also sounds like the heatrange is different .

it may just foul up easier or missfire , or at worst the electrode could overheat and break off or burn a piston .
if it was my engine I wouldn't risk the wrong plugs especially in a 2 stroke

[ian parkes]

Stephen
you might find these guys helpful . i have used them for unusual plugs before and they were very helpful . There is also an on line chart of superceded plugs and explanations of plug types etc .

www.spark-plugs.co.uk

Maybe some iridium plugs or wire centre electrode type would help with the oiling up

[MarkM]

On this site http://bbcboards.zeroforum.com/zeroforum?id=51 Seahorse says this:
"Johnson-Evinrude Factory Spark Plug Chart"

[BogMonster]

Heard back from Oakleys and the answer basically said "whoops"

Apparently the plug fits some other J 115hp but not my one and I now have a chart showing every plug for every type of Johnson O/B!

Thanks for the help

[PeterR]

Originally Posted by BogMonster

Heard back from Oakleys and the answer basically said "whoops"

Apparently the plug fits some other J 115hp but not my one and I now have a chart showing every plug for every type of Johnson O/B!

Thanks for the help

Does this mean they are going to help out in any way

[BogMonster]

Originally Posted by PeterR

Does this mean they are going to help out in any way

Yes he said I could send them back though the "correct" ones are apparently a bit more expensive. I've also had them for well over a year - just did a "spares order" when I bought the boat, for stuff I thought I might need i.e. gear oil, plugs, water pump impeller etc etc so I had it on hand. Only just got around to needing them!

[Locozodiac]

With refference to the posted spark plug thread :

QL 78 YC Stands for:
Q=Resistor
L=14mm thread
78=Special Application Plug
Y=Standard Proyected Cone Nose
C=Copper Design

QL 77 JC4 Stands for:
Q=Resistor
L=14 mm thread
77=Special Application Plug
J=Ground Electrode Modified Gap
C=Copper Design
4= Wide Gap Required

One is warmer, the other colder, you should clean and gap your plugs according to your engine service manual at least once every 50 working hours, 2 stroke engines tend to literally eat the internal electrode quicker than 4 stroke engines, so constant re gap as specified to obtain best engine performance. It's normal to see some plugs more fouled than others, so rotate the plugs in each service.

To fight corrossion spray a generous amount of WD-40 on the plugs when new and re spray on each service. Maybe you should try the warmer ones in winter and colder ones in summer previously gapped correctly. The QL77JC4 is the second alternative termal range to the QL78YC.

Locozodiac

[BogMonster]

Thanks. Would I be correct in thinking that too big a gap (due to electrode erosion) means a weaker spark and thus more of a probability of fouling on a 2 stroke? It would tally with my recent experience prior to changing the plugs the other week - I haven't been out again since to see if it is any better. The plugs had eroded to around 40 thou clearance (should be 30 or 32 depending on what figures you use).

[Locozodiac]

A bigger a gap means weaker spark on the electrode, that's why you need to re gap more often to obtain optimal gasoline consumption and engine performance. In the long run will cause more plug oil/carbon fouling, have a proper oil/gas mix ratio too so both issues help the engine perform at it's best.

In my particular case my plugs are used max 150 hours, re gapped, cleaned and rotated each 50 working hours. Dispose off properly, put new ones and so on. It's a good idea to use an engine hour meter to control exact working hours and perform scheduled maintenance.

[jwalker]

Following Champion's numbering sequence, the higher the number the hotter the plug. So your 77 will run a bit cooler than the 78 and the standard nose will be more prone to fouling. This doesn't mean you can't use them. Running hotter plugs in an engine is to be avoided but running a cooler plug will do no harm. If it were me, I'd gap them to 30 thou to keep the spark fat and use them. If they foul too often you've lost nothing cos I wouldn't reckon it is worth the cost to return them.

For info, NGK plugs get cooler as the numbers increase whereas Champion plugs get hotter as the number increases.

A cooler plug has a shorter heat path to the body.

[BogMonster]

Thanks. The book says the gap should be 0.8mm or 30 thou but 0.8mm is actually 32 thou which is what I did them to, so I think I will re-do them to 30 and see what happens.

I guess these plugs have done a bit less than 100 hours, not sure when I changed them exactly (the engine does have an hour meter just didn't note it down) and have eroded 10 thou in that time so I guess every 3 months or so wouldn't be a major inconvenience. The plugs I took out about a year ago, still in there from the original owner had been in there for aeons, they were burnt to a crisp and when I tapped the ground electrodes, they fell off on 3 of the 4 plugs ... lucky I checked it when I did

[jwalker]

Originally Posted by BogMonster

...when I tapped the ground electrodes, they fell off on 3 of the 4 plugs ...

Feck! Maybe the cooler plugs will be better in your motor, it sounds as though it gets kinda warm in your cylinders.

[BogMonster]

No sign of problems with the current plugs I had in there until the other day - they all look healthy apart from the one that was fouled and that was just wet with fuel. I think the ones dating from the previous owner had just been in there rather a long time