plugs for 1957 Johnson 10hp QDL-18

JBrit12

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Hey guys, conflicting information here so this is what I got. My old plugs still have spark but I want to replace them during this rebuild since tank, coils, lines, have all been replaced and carb almost rebuilt. The current ones I have are J6C and from what I read is pretty much the recommended plug and I know I can find them online. However, I ran to the autoparts store to pick up the last couple things I needed to try to fire it again (gas lines for engine, another bottle of carb cleaner, gasket sealer for tank if needed, etc.). They didn't have J6C and said the computer was telling them J8C so I bought a pair but did my homework when I got home after I asked them if I could return them and I'm seeing it is not recommended for using J8C. Actually, seen most say not to use those but a couple saying it would be OK. I certainly don't want to use something I'm not supposed to so what are your thoughts. I'm far from a professional engine guy, especially one that is 60 years old. Thanks.
 

HighTrim

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WIsh I could tell you to use them, but they are too hot a plug. I would not. Get the J6C or the NGK equivalent
 

oldboat1

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Don't use the J8s (too hot). Exchange them for J4C -- J6 will do, but J4 is really what you want. Gap at .030.
 

JBrit12

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OK, sounds good guys. I'll exchange them tomorrow if they have them or I'll refund and hit another parts store. Thanks.
 

oldboat1

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Yeah, not contradicting HighTrim on the plug choice (I've used the J6s) -- not a lot of experience with the NKGs in my '50s motors, so will defer.
 

Joe Reeves

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OK, sounds good guys. I'll exchange them tomorrow if they have them or I'll refund and hit another parts store. Thanks.

Been with OMC since 1960, retired in 1991... OMC's recommendation is the Champion J4C plug with the alternative being the J6C, both gaped at .030. The J6C may provide slightly better performance. Use either with full confidence.... and No Other!
 

JBrit12

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JBrit12

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Been with OMC since 1960, retired in 1991... OMC's recommendation is the Champion J4C plug with the alternative being the J6C, both gaped at .030. The J6C may provide slightly better performance. Use either with full confidence.... and No Other!


Thanks man, almost certain I'll go with the J6C then. Just hope I can find them in town rather than waiting for another online delivery, haha.
 

oldboat1

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Here's some info that might be useful (cited in the stickies here at the top of the forum): http://www.fiberglassics.com/library/images/2/2a/Evinrudeservice001.pdf

There is a wealth of great info. on the the Ramblings site, so wouldn't steer anybody away from there even if I disagree with bits and pieces of the advice or recommendations. Note the busted up piston pictured on the link you provided, and the cause. The motor should be run with a 24:1 mix. Going to a hotter plug can mask other issues, IMO, typically ignition or carb. Unfortunately, people who don't know these motors sometimes want to go to either a leaner ratio or hotter plug. In fact, the motor will run extremely well with the richer mix (richer by current standards) and the recommended plug(s).

I look for good operation with a lean carb setting -- rich fuel ratio, lean carb air/fuel setting. That means a squeaky clean carb, and a strong ignition -- not all that hard, and good fun getting there.

I'm a fan of the original fuel system (pressure tank), btw, although lot's of guys do well converting to a fuel pump. (OMC offered that as a '57 option for the 35s.)
 

HighTrim

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Any reason oldboat as to why go with J4's instead of the J6's? Just wondering, don't know much about this topic.

Here were my references http://www.leeroysramblings.com/johnson_QD.htm
http://www.*****************/parts/c...lug-guide.html
and from a couple other forums

It really depends on what you do with the motor.

The J4s are a colder plug. Better for a lot of Wide Open running.

The J6s are a hotter plug. Better when mainly trolling.

I run ALOT of 50s OMCS, and I personally buy J6Cs buy the box. I just find they are a better all around plug than the J4Cs in general for the boating I do. Your opinion may vary. Don't get me wrong,I use the J4C in a lot of my motors.

For best results, run the motor, and inspect the plug. Should come out a golden type honey colour. Adjust plug from there either up or down.
 

JBrit12

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Tough choice, probably not a lot of trolling, more running to spot and drifting or using electric trolling motor but also not a lot of long trips at full throttle either since it's companion boat is only a 14' aluminum Starcraft from back in the day and not able to handle large bodies of water (waves). I guess I could eventually try both plugs if it sees the water enough to gather that much data. My hope is, that even though my father's health is failing, having these beauties back up and running again will motivate him to want to hit the water like he did when he was a lot more youthful and able bodied. I know he is appreciating my efforts and time in this and that is all that really matters to me but I'd like to ice the cake with a big ole smile on his face if I could get him on some fish and back home with a sore arm!

I really appreciate your guys' time, responses, and knowledge. I can catch fish with the best of them and most species but I've only recently got into the mechanic side of things. Personally I'm enjoying it but also couldn't have done it with some reassurance from guys like you all, so again, thank you and I'm sure I'll be posting some more and will hopefully have this old girl back to life and breathing again pushing a nice wake across some body of water come spring time. Before then I'll probably be asking a few questions about replacing the wooden trim around the edge of the aluminum Starcraft.
 

Chinewalker

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+1 to what HighTrim said. I've fouled J4Cs a few times, especially since I run my 1950s motors fat on the oil. I've found that J6Cs are less prone to fouling...
 

Bonaventure

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Do take care installing that you do not go too tight. I don't know if they have a steel insert in that model of motor, but I have seen the plug threads stripped on a few heads that have only the aluminum for threads. I believe about 20 ft/lbs would be maximum. If you don't know the torque, you should maybe do a post to find out.
 

lindy46

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J6C is a good overall plug, and I use them on most of my 50's-60's Johnnyrudes. You can get them at O'Reilly's.
 

JBrit12

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Well apparently you can't get them at my O'Reilly's as I was just there and the plugs he gave me saying were correct aren't even close so those are getting returned here in a few minutes. Can't wait to see this jerk again, literally, he was dropping F-bombs while I was down one of the isles. Looks like I'll be ordering online.
 
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oldboat1

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Clean up your J6C plugs and regap -- should be good to go. I clean them off with some carb spray, then lightly polish the contacts with some sandpaper.

I was tinkering with a motor this afternoon, and thought I should check my stock -- find I'm still using NOS J4Js and J6Js. The side electrode on the old plugs extends only about half way over the center electrode, and may be a little less prone to fouling.
 

JBrit12

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Well, I think I finally caught a break. When taking back the plugs that obviously were incorrect for the 2nd time, I once again was being helped by the rather uninformed and unprofessional F-bomb dropper kid who proceeded to insist that what he just pulled up on the computer was the one he should have gave me the first time. I finally told him, dude listen, you have no idea how important this is here. It is an antique motor that I'm not about to fire up on some guy's whim or guess. What I really need is a Champion box that reads J6C on it or J4C or I'll just order it online. He kept saying that the exact equivalent would be there in the morning on the truck. Then some older gentleman steps in and asks what the dilemma was and I told him some of the story and he walks out back and flops a J6C on the counter so I asked if he had another and he said I got 8 so he got me another, lol. After talking with him it was apparent he knew a little bit about old stuff and even recommended that I run rec gas too. I told him that was the plan eventually.

oldboat: You are gonna laugh, but I got looking real close at the plugs that were already in the motor and I actually think they read J6J or J8J or something. I know the ones I got are the same from the bolt toward the business end but maybe 3/16" longer on the boot end. My father and I are certain that some work had been done to the engine at some point (probably just great grandpa tinkering as there were a couple missing screws on one of the bracket things that hold the carb and faceplate) but unless that is the same plug with a different reference number from 35 years ago he may not have even had the right ones in there. So hopefully, if they are the equivalent of a J8C in today's standards no damage was done back then. I know my father said that grandpa told him it always ran great as long as you were on one setting for slower speeds and another for higher speeds. I guess I'll be finding out. Tomorrow I will put the carb back together with new gaskets, needle, needle seat, float, clean out the glass bowl, and blow all the ports/holes out with compressed air and it will be time to try it again. I also have to get the new impeller in as well and double check gaps on points and plugs. I'll let you all know how it goes.
 

racerone

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In simpler times like the late 1960's we used J4J if motor had a thermostat.---We used J6J if there was no thermostat.---------Never had any complaints at all.---------J4J is now marketed as J4C
 

Tech Tony

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Apr 30, 2016
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You can use Autolite 303 plugs. They are the equivalent of j6c. AutoZone carries them . I have them in my qd17 they work great.
 
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