15R75c plug confusion

[OLDIRON]

Ok guys,here's the deal.Motor came with Autolite 45 badly fouled.Went to get new plugs,and lots of other things.FSM says to use UL4J,nomenclature plate on motor says to use L7J.So I go with the L7J,discontinued.Guy at Napa says this NKG B7HS will work.They do,and work fine,until I run SeaFoam through it.Motor runs way better,but plugs don't look so good.So I figure get a new set of plugs,but I'm gonna go with the right ones for the motor this time,no Napa.Go to a local marine repair,and he says they should be a UL81C.Put those in,and this thing that now always started on the first or second pull,woun't start unless I have the throttle WO.So I clean up the NGK B7HS,and guess what? Even not so clean,she starts right up,and runs great.Took it out on the river last week,never missed a beat.
So I guess my question is,If it runs good on these NGK's that are not that clean,should I just bypass all this Champion mumbo-jumbo and stick with a new pair of NGK's? Your thoughts please.

 

[JB]

Re: 15R75c plug confusion

It was designed to use Champions. That is what I would use.

 

[OLDIRON]

Re: 15R75c plug confusion

It was designed to use Champions. That is what I would use.

That's my thinking,but they don't make them anymore,or atleast not the exact match.I'm leaning to the NGK's.Even dirty,they seem to run the best.

 

[tashasdaddy]

Re: 15R75c plug confusion

here is a fairly up to date chart http://www.boatsetup.com/SparkPlugChart.pdf the dealer is correct.

 

[OptsyEagle]

Re: 15R75c plug confusion

I would be curious to hear from anyone that owns a 1974 to 1976 9.9Hp/15Hp Evinrude or Johnson that actually uses the champion UL81C plugs with successful operation.

I too own a 1975 9.9Hp Evinrude (identical to the original poster) and found that when I used the UL81C plugs my motor bogged down, then surged and bogged again (I believe this to be one cylinder failing and then firing and failing again, etc). I checked my spark and it jumped a 3/8" gap no problem. I changed the plugs to newer UL81C to confirm if I had a bum plug with the same response. I then changed the plugs to the NGK B7HS and the problem went away completely.

I have noticed a few other people on this board having similar issues with the UL81C plugs in these motors, but of course you only hear about the problems on this board, not the successes. It makes no sense, I know. I use champion plugs in other motors with no problems, but I can't seem to get the Champion UL81Cs to work on my 1975 9.9Hp Evinrude.

If you are using the UL81C plugs successfully, my next question would be, when was the last time you changed your coils? I suspect that perhaps I may be using the original coils (acquired the motor about 4 years ago) and perhaps the champions need a slightly higher voltage than the NGKs. If my coils were putting out a weeker spark on the champions, it would not only help explain my condition but also why the original poster needed a little more gas to ignite things. I am reaching here since it is quite confusing. My motor is working well with NGKs so it is not a big issue, but it is something that has perplexed me for quite a while.

 

[F_R]

Re: 15R75c plug confusion

I was a dealer mechanic when that motor was built. I can tell you that we had a LOT of spark plug troubles with them. Some motors we couldn't keep running for one weekend. Mind you, these were brand new motors. OMC came out with a number of "fixes" for the problem, including different cylinder heads, different carburetors, different plugs, different mag plates, etc. None of them worked worth a hoot for very long. I would send the motor out as "fixed for sure this time" on friday and it would be back on monday morning with fouled plugs.

So, with that history, it is no wonder there is confusion as to what should be the correct plug. And no wonder the plug charts are all different.

In 1976 they went to CD ignition and were able to use different plugs, but those plugs won't work in your magneto ignition because you don't have enough spark voltage to fire them.

So, what's the best plug choice for your '75? I dunno because I "retired" from the shop in 1978 and the problem with the '74 and '75 wasn't fixed yet, even then. I guess whatever works best for you. But don't expect to be able to use surface gap plugs.

 

[OLDIRON]

Re: 15R75c plug confusion

Thanks.The mechanic told me these 2 years were plug fouling SOB's.
I think I'm gonna roll with the NGK B7HS. They seem to perform the best,even when dirty.Normaly I would stick with Champions,but not in this case.

 

[marcysibyll]

Re: 15R75c plug confusion

I've got a 72 20HP rope start. Pretty much the same as the 9.9-15 hp family?I am using the NGK's. Runs so good, I don't want to touch it. Don't want to clean carbs,clean plugs or nuttin.
Had a new set of Champions leave me in the middle of Shawano Lake a few years ago.

I sold car parts for 25 years. I got to beleive that engines are stupid. They don't know what plug is screwed into them. Got Autolites in my Goldwing. If you stay in the engine manufactures heat range for that engine (any engine) you will be good to go.

 

[Silvertip]

Re: 15R75c plug confusion

As a snowmobiler and boater since Hector was a pup, I will add my two cents worth on my feelings about surface gap plugs. I hate them. I had trouble with them on snowmobiles and my Merc outboard (75 HP 3 cyl) would load up on them periodically as well. Another contributor on this board and I have run conventional plugs in both motors with excellent results. Better performance, better starting, better idle and more revs at WOT. Just be careful what heat range you stick in the engine.

 

[captk]

Re: 15R75c plug confusion

I used to have a 2 thirsty five (235) v6 mid 80's that would eat Champs in 10 hours. switched to ngk, at the advise of my omc service rep. and never had any more issues. 74 to 76 , 9.9 / 15 with low tension ign. systems are temperamental at best , if the ngk plugs match heat range use them.

 

[OLDIRON]

Re: 15R75c plug confusion

I would be curious to hear from anyone that owns a 1974 to 1976 9.9Hp/15Hp Evinrude or Johnson that actually uses the champion UL81C plugs with successful operation.

I too own a 1975 9.9Hp Evinrude (identical to the original poster) and found that when I used the UL81C plugs my motor bogged down, then surged and bogged again (I believe this to be one cylinder failing and then firing and failing again, etc). I checked my spark and it jumped a 3/8" gap no problem. I changed the plugs to newer UL81C to confirm if I had a bum plug with the same response. I then changed the plugs to the NGK B7HS and the problem went away completely.

I have noticed a few other people on this board having similar issues with the UL81C plugs in these motors, but of course you only hear about the problems on this board, not the successes. It makes no sense, I know. I use champion plugs in other motors with no problems, but I can't seem to get the Champion UL81Cs to work on my 1975 9.9Hp Evinrude.

If you are using the UL81C plugs successfully, my next question would be, when was the last time you changed your coils? I suspect that perhaps I may be using the original coils (acquired the motor about 4 years ago) and perhaps the champions need a slightly higher voltage than the NGKs. If my coils were putting out a weeker spark on the champions, it would not only help explain my condition but also why the original poster needed a little more gas to ignite things. I am reaching here since it is quite confusing. My motor is working well with NGKs so it is not a big issue, but it is something that has perplexed me for quite a while.

Well,I think FR here,and the mechanic I talked to,pretty much nailed it.The 74 and 75 9.9 and 15's fouled plugs.Period.By the way,I put new coils in mine,so I don't think having older coils is an issue for you.The mechanic told me that these motors have a weak spark,but still sold me the ul81c's only because that's all he could sell me,and still comply with being a dealer.CYA,I think they say.

 

[OptsyEagle]

Re: 15R75c plug confusion

Thanks OLDIRON, that takes care of that idea that it might be my coils.

I have put many hours on my motor with no problems using those NGKs but I still keep a spare set and a socket wrench in the boat at all times. I am getting too old for rowing. You may want to do the same. Happy boating to you.