Spark plug temperature range?

[Tony]

I'm running slightly rich, and thinking about switching to a hotter spark plug.
Currently using Champion RV15YC4, may switch to Champion RV17YC, which is two ranges hotter.

One guru friend has recommended this to me, while another guru friend says do not! I am conflicted...any thoughts?

[txtaz]

I'm no pro here, but you could always lean it out. When I built my engine in another boat I was warned not to run too hot on the plug or I would burn a piston.
Wes

[Rootsy]

you need to get someone who knows what they are looking at to really "read" those plugs... you can tell 3 or 4 things from a plug other than just rich or lean... the plug will tell you fuel mixture, ignition timing, heat range, etc etc...

takes a very good light and a loupe.

[MOP]

Tony give use some idea of why you feel you are running too rich, true I had commented on the slight black ring on your tips at 1K. I also get a slight ring on mine, my plugs read dark but well within a color range I have become used to. When we were looking for the possible cause of your over heating at 1K I hung my skinny bod over the back looking aft at all speeds and felt for hot spots and found the leaky risers, that another story. When you nailed it there was no smoke what so ever, it runs like a bear and sounds great. Unlike a street engine marine applications normally run on the rich side the plugs will show a fair bit darker, they have to due to the high load they constantly run under. I am against going up on heat range having seen the problems it can cause, burned pistons, scuffed cylinders ETC. I would try fooling around with gap or another make plug. RV15YC-4 or MR43T's are the best plug for you 302, you could also try the eqivilant NGK's they have a broader heat range. If you have a digital camera shot some close ups of the plugs and post them, the best reading is obtained by running hard (4000+)for 2-3 minutes then doing an immediate shut down with no -0- idle time pull then the plugs.

Phil

[GKricheldorf]

Here is a link with some good pictures on plugs. Maybe you can find yours.

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

[turbo2256]

That link shows little about plug reading for fine tuning idle timing ,total timing, idle mixture, cruse or full speed. Always go with colder plugs when tuning untill you got it closer to right would rather foul a plug than burn an engine.

[MOP]

GKricheldorf thanks for posting the chart, it is one of the best I have seen. The text is good and will help a lot of people to determine what they have.

Phil

[Tony]

Phil, thanks for the timely advise and sound reasoning. I am sticking with the original RV15YC4's, and will check them soon. The recommendation to switch was based on only one plug, the stern port side, I believe #8. It was the worst, looked very fouled, while the others turned out to be not so bad.

Jamie, I did what you said and took all the plugs to the shopo who bult my engine, they are Ford fanatics. They did not see "fouled plugs" and also advised to stay with the same range plug.

The bowl levels on my Holley were way high, despite turning the adjusters all the way down. So we pulled the top of the carb apart and bent the thin metal tab that the adjuster pin hits, now we have the levels right on the money. This is what likely "washed the rings", resulting in my oil consumption problem.

Thanks a ton for the link, and all the good advise. We're off to Torch Lake for te weekend, hopefully all will go well!