Re: Enlighten me about spark plugs

[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