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Author Topic:   spark plug 101 help
Cpt Quint posted 03-11-2003 10:48 AM ET (US)   Profile for Cpt Quint   Send Email to Cpt Quint  
picking up extra set for 50 rude. Champion in there now with no problems. Question is the book says Champion part mumber (821-1).
The number on my plug itself is not the same. My plug now is QL78C and the reference part # 821-1 reads L77JC4. I have no clue as to what the difference is between QL78C, and L77JC4?
Any easy way to read what these mean and if swaping the QL78C with the L77JC4 is okay for my motor??
whalersman posted 03-11-2003 11:29 AM ET (US)     Profile for whalersman  Send Email to whalersman     
Cpt Quint,

I have been using the QL77JC4 in my 1985 Evinrude for years now..

The "Q" stands for Resistor which reduces noise for Radios...

The "C" stands for Copper tip which is recommended.

I believe the 77 is for susatined Low Speed running.
The 78 is just a little hotter plug.

I also run the QL77JC4 in my 1985 150 HP Evinrude and my 1988 8 HP Evinrude.

My mechanic advised me to run the QL77JC4 gapped at .030

whalersman posted 03-11-2003 11:52 AM ET (US)     Profile for whalersman  Send Email to whalersman     

The 78 is a little colder plug for sustained High speed running.

I just replaced all my Spark Plugs and checked the factory gap.... They were all gapped right at .030 except for one or two which needed a little adjustment.

Q = Resitor
L = Reach
77 = Heat Range
J = Cut back ground electrode
C = Copper Tip
4 = Wide Gap

Bigshot posted 03-11-2003 01:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Everything from about 1978 to present runs the Ql77JC4 plugs or just drop the Q if no electronics, etc. There are cross references for other plugs but with every OMC I have run the L77JC4 is awesome. So you know I HATE champion plugs but they work great in lawnmowers and OMC outboards......hmmmm!

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