Enlighten me about spark plugs

[retiredoz]

Well, give it a shot and see what happens ? At least, thats what I’d do…

[chris-p]

Yeah I know a lot of guys poop on Champions for some reason, but NGK is not some magical plug. I buy the J6s and J4s by the hundred box and can only think of one problem Ive had. Not against running other brands either, if I have them.

[legendre]

quote thepetrolist:

quote Pappy:

quote legendre:

It’s possible that the hotter plug caused a slight overheating condition which resulted in vapor lock, stalling the engine.

Talk about the need for enlightenment…….!!

Yeah, well, I guess you’ve never been a newbie and never made mistakes?
And sometimes ones brain farts and can not for the love of something figure out whats wrong.

I’m only a ‘newb’ as pertains to OBMs – my experience is very limited in the area. That said, I have more than a dozen or so years working in and managing motorbike service shops, and decades playing with my own toys – so if anything, I’m more qualified as an old fool. 😉

Back on point..

Spark plug heat range controls more than just the temperature at the spark plug’s tip. It also has an effect on the peak temperature of the combustion chamber, and more importantly – the flow of waste heat through and out of the motor.

Colder plugs run cooler, by virtue of being more efficient at passing chamber heat into the cylinder head and then to atmosphere via the cooling fins or water jacket. Hotter plugs not only run hotter at the tip but also are less efficient in conducting heat away to the head & atmosphere – but the engine still has to get rid of that heat some way.

One way it does this, is by releasing more of the heat in the exhaust gas.. which increases exhaust manifold temperatures. In an outboard design where the exhaust manifold is closely-coupled to (sometimes even an integral part of) the intake system, this can lead to higher temperatures in the intake, carb and fuel lines, particularly if the lines are copper.

Anyway, I’m not sure what folks are objecting to.. so far, I’m the only one to have stuck-out their neck and posited a hypothesis as to why plug heat range alone might have stalled the OP’s motor. Feel free to knock it down, that’s fine, but it would be helpful if you also offered a competing hypothesis..

-L

[thepetrolist]

Ah, I see!
Thanks for the clarification.

Today I once again bought some new plugs. Luckily I work at an auto supply store so I can check up on plugs while at work. 😀
We were out of NGK B7S and Champion J4C’s but I got Denso W22S-U:s . They matched the specs so I thought I’d give it a shot. Installed them, pulled the starter.. And off they went! Ran better than ever before, both the HD and the Sportwin. Which brings me back to the thought about the Bosch W8EC plugs being dodgy. But what is the chance that FOUR brand new plugs are bad?
Any other thoughts?

Just for the heck of it I also got a denso M17 for my ’67 Seagull and that too ran much better than before.. But that engine ran a 40 year old Bosch M45 so no wonder..

[pappy]

Let me simplify this for you although with a simple Google search you could have avoided printing the mis-information yourself.
http://matchlessclueless.com/mechanical … mperature/

Secondly, give us an example on an outboard where the intake is closely couple to or an integral part of the exhaust. Most I have seen have the intake on one side of the cylinder and the exhaust on the other.

The point here is that folks are here to learn FACTS about their outboards. If you know something as FACT, fine, post away. If not, bear in mind that you are possibly misleading those who are here to learn and worse yet, cost someone money and time following that misinformation.

[thepetrolist]

quote Pappy:

Let me simplify this for you although with a simple Google search you could have avoided printing the mis-information yourself.
http://matchlessclueless.com/mechanical … mperature/

Secondly, give us an example on an outboard where the intake is closely couple to or an integral part of the exhaust. Most I have seen have the intake on one side of the cylinder and the exhaust on the other.

The point here is that folks are here to learn FACTS about their outboards. If you know something as FACT, fine, post away. If not, bear in mind that you are possibly misleading those who are here to learn and worse yet, cost someone money and time following that misinformation.

Talking to me here..?

[pappy]

Nope

[thepetrolist]

quote Pappy:

http://matchlessclueless.com/mechanical … mperature/

Nice, thanks for the link. Gonna give it a thorough read-thru

[legendre]

quote thepetrolist:

Ah, I see!
Thanks for the clarification.

Today I once again bought some new plugs. Luckily I work at an auto supply store so I can check up on plugs while at work. 😀
We were out of NGK B7S and Champion J4C’s but I got Denso W22S-U:s . They matched the specs so I thought I’d give it a shot. Installed them, pulled the starter.. And off they went! Ran better than ever before, both the HD and the Sportwin. Which brings me back to the thought about the Bosch W8EC plugs being dodgy. But what is the chance that FOUR brand new plugs are bad?

The chance of four brand-new spark plugs – made by two entirely different manufacturers – being ‘bad’ out of the box is pretty slim. Of course, in a two-cylinder motor, all it takes is +one+ bad plug to make things go awry.

quote :

Any other thoughts?

All I can tell you is that there most certainly +is+ an answer, and with the proper knowledge and instruments, it could more than likely be found. But I sure as heck can’t tell you, not from where I sit, way out here in the cheap seats.. 😉

And again, I’ve simply had crap luck with both Bosch and Champion, in all but a few previously-described situations. All plugs pretty much look & feel alike, but there’s some very serious and subtle science going on in those things.. a wide-world of trade secrets, I’d wager.

[jim-moffatt]

I’ll try to explain what happens if you use plugs that are too hot. I have experienced this on two motors.
At full speed the plugs get to hot and the mixture pre-ignites resulting in a drop of rpm to a much lower speed. Then
since there is less heat the plug cools off and the motor starts running faster. On a 3.5 Chrysler air cooled motor it cycled over and over.
On a Johnson A-50 the cycles were less clear but it did not run well.

On the Chrysler I had inadvertently installed a H10C instead of the correct H8C.
On the A-50 I was simply experimenting. I tried D9s, D14s, D16s and D21s.
Ended up using D16s.

[Author]

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