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  Spark plug selection: hotter or cooler?

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Author Topic:   Spark plug selection: hotter or cooler?
ShrimpBurrito posted 03-04-2003 07:45 PM ET (US)   Profile for ShrimpBurrito   Send Email to ShrimpBurrito  
I've always replaced the spark plugs in my 1987 40 HP Johnson with what was in there before. However, according to the dealer, it turns out there are two recommended Champion plugs indicated for this engine: Champion L82YC ("L") and Champion QL77JC4 ("Q").

It's my understanding the Q is a hotter plug, and offers more protection against fouling when idling or trolling. The L is cooler, which the dealer recommended using if you run the engine hard.

A few questions:

1) Is Q really hotter than L? Are there other substantive differences?
2) I don't troll too much, but do run ~10 knots a good amount. It seems everyone would want to protect against fouling, so I'm wondering, "What are the disadvantages to running with Q, the hotter plug?"
3) Conversely, what are the advantages to running the cooler plug, L? More power? Less wear on the engine?

Has anyone seen a site that gives a good lesson on what the differences with the spark plugs mean, and how to distinguish them by their numbers? Please share your wisdom!

newt posted 03-05-2003 08:46 AM ET (US)     Profile for newt  Send Email to newt     
Shrimp, I used to own and race a 2 stroke yamaha streetbike. I always ran the cooler plugs because I always rode with the RPM's up high.

http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqheatrange.asp

http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf

Arch Autenreith posted 03-05-2003 10:50 AM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Great info on that website, Newt. Thanks.
ShrimpBurrito posted 03-05-2003 02:26 PM ET (US)     Profile for ShrimpBurrito  Send Email to ShrimpBurrito     
That is a great website, indeed, Newt. Thanks for posting it. NGK's Australian site has even more info.

http://www.ngkspark.com.au/tech_info_spark_plug_index.htm

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