Spark Plugs

[perkdp]

I'm looking for recommendations on spark plugs for these motors. I realized last evening that a spark plug can play a big role in engine performance. Till then, I thought a spark-plug was pretty much a spark-plug. <br /><br />1971, Johnson 4 Horse <br />1973, Evinrude 18 horse

 

[R.Johnson]

Re: Spark Plugs

Champion, J4C for both.

 

[perkdp]

Re: Spark Plugs

Hmm, I put a new set of J4C in the 18hp and it didn't run good at all. Borrowed the set of J6C from 4-hp and put in the 18-hp and it ran good. New plugs DOA ? <br /><br />Central Arkansas. Temp in the 80's. <br />Air Temp Range the motor will run in will be 30 - 100 degrees f. <br /><br />Average air temp will be in the 70's

 

[R.Johnson]

Re: Spark Plugs

Have you checked the thermostat in the 18? Is it coming up to temperature?

 

[perkdp]

Re: Spark Plugs

No, I haven't. I was looking to the thermostat to be open and keep it cool more than the opposite. <br /> <br />But I don't the the J4C plugs I had in it weren't running well enough to bring it up to temp. <br /><br />If the thermostat is stuck, how does it affect the bypass indicator on the rear of the leg ?

 

[R.Johnson]

Re: Spark Plugs

The J6C plug was used in the engines without a thermostat, as it is a slightly hotter plug. I take it your running problem is at idle. A stuck thermostat will not show at the tell-tale stream. If the engine is slightly warm at idle, the thermostat is stuck open, or leaking around it'seals.

 

[Paul Moir]

Re: Spark Plugs

The 18hp doesn't have a tell tale as such, but rather a water outlet. Almost all the cooling water exits through that outlet so it does give you some idea of how the thermostat is operating.<br /><br />I find the recommended J6C works better in my 4hp. Those don't have a thermostat.<br /><br />The difference between the J4C and J6C is the heat range, which is the temperature range the porcelin nose of the spark plug operates at. That temperature is not achived until the engine has run for a bit and the head & plug body temperature stablizes. If the plugs are not allowing it to run even until this happens, something is wrong with the plugs. Check the gap (.030") and try swapping the J6C one at a time to see if you have a bad plug.

 

[perkdp]

Re: Spark Plugs

Hmmm..... scary. How do you tell if the thermostat were to stick closed since these motors don't have a temp guage ? <br /><br />Leaking around which seals ?

 

[perkdp]

Re: Spark Plugs

I kinda did the swap out thing. <br />Had it running,, one was only firing part of the time. Swapped one of the J4C (new) for the use J6C (only option at the moment) it helped some so I borrowed the other J6C to make a pair. <br />That's what seemed to make the difference. <br />(I am very confident that one of the J4C just bought for the overhaul was either DOA or fowled by other conditions). <br /><br />What do you think about running the J6C in both 4 and 18 ? <br /><br />Clymer manual recommend J6C for the 4hp <br />OMC shop manual recommends J4J or J6J for the 4hp<br /><br />Clymer manual recommend UJ4J for the 18 hp <br />and it runs pretty darn good with the J6C .

 

[R.Johnson]

Re: Spark Plugs

Perkdp: I should not have said seal's, as there is only one. It is a rubber seal ring that is a stretch fit around the thermostat. On an over-heat, generally the engine will discharge steam out the relief Paul discribes. It is really not hard to fit a tell-tale to these engines.

 

[perkdp]

Re: Spark Plugs

Gotcha. <br />I had a dicussion with a fella a few days back who was going to send me a drawing and parts list for a tell-tale (pee-hole i've heard it called). <br />If the by-pass shows good circulation and no steam I guess that works for me but if it is really simple to add a tell-tale that's after the thermostat in the circulation path, I'd consider adding it. <br /><br />So, now we've kinda switch subjects. <br />Let's jump back to the plugs....... do ya'll think there's danger in running the J6C plugs in both the 4 and 18 ?

 

[Paul Moir]

Re: Spark Plugs

It should really run fine on the J4C. The application chart in the 2005 BRP service parts catalog lists that as the plug for your engine. I don't know where Clymers gets UJ4J, perhaps it was some older recommendation. <br />The J6C is optional, you may find it works better when you're idling for a long time. I guess other factors can demand it too such as low compression or high altitude. I really don't know much about that latter subject.<br /><br />EDIT: A tell-tale comes before the thermostat. The water exit on the back of the engine is after the thermostat (& bypass).

 

[perkdp]

Re: Spark Plugs

Thanks Paul, I'll get a new set of J4C and see how they work. I wouldn't consider this high altitude. Possibly compression issues, I've not run a test, maybe rings not seated good yet, maybe cylinders....(this is the basket case you've been helping me with. since my post a few days ago thinking all was good, i've had a dead cylinder (no spark) traced to a condenser, new points and condenser, now plugs. the plugs could have lead me the points and condenser) <br /><br />J6C is the Hotter of the two ?

 

[perkdp]

Re: Spark Plugs

interesting.... the brp (evinrude online diagrams) show the following for my model 18304A<br />D# P#<br />31 0385930 Desciption<br />Add to pick list SPARK PLUG, Champion UJ4J <br /><br />But it only shows it used in 1973 and 74 in the 18 - 25 hp motors.<br /><br />I found a web link to a sparkplug recommendation / xref in a post here at iboats but now I can't find again. Anyone know the link ?

 

[Paul Moir]

Re: Spark Plugs

Yes, J6C is the hotter. The UJ6J had an auxiliary gap, which is proported to improve fouling resistance. The earlier 18hp engines used the plain J6J, which differes from the modern J6C in that it's ground electrode is cut back so it only half-covers the centre electrode. This is supposed to help with fouling too.<br /><br />With the limited number of 2-stroke engines available, as well as the improvements made in modern engines and oils, Champion is not offering these 2-stroke specific plugs anymore.<br /><br />This website seems to keep their spark plug chart reasonably up to date:<br />boatsetup.com/SparkPlugChart.pdf<br /><br />Champion's chart is riddled with errors, and following their recommendation can lead to severe engine damage.<br /><br />If you're plugs are failing due to carbon fouling, it should be obvious. There should be hard carbon deposites on the insulator which are shorting out the centre electrode.

 

[perkdp]

Re: Spark Plugs

Thanks.<br />I'll check that link. <br /><br />No carbon build up. Too new.