Spark plug question for 1987 Mercury 25 hp 2 stroke

seanymph85

Petty Officer 2nd Class
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Nov 5, 2013
Messages
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Hopefully this is the right category for asking this question and hopefully someone may know the answer as obvious as it may seem to others with far more knowledge and experience in this area then I have.

The PDF user manual I have for this motor cals for either NGKB7HS, Champion L82 or AC S41F plugs. I found there were 2Champion L78YC plugs in the motor as purchased. The threads on the plug appear to have the same reach as the new correct plugs however it has been more than a few days since the motor was running to get some Stabil treated gas run into the motor in preparation for winter storage. It was still wet and smelled strongly of gas. I am wondering if anyone knows on the technical side of things what someone having used the L78YC plug would have had on operations as compared to the L82 in this 2 cylinder 2 stroke outboard. serial 0B236228 model 1025577 version ELH I might have been able to figure it out if I knew things like heat range, resistance factors etc. on either of these plugs but can't discern that with my limited knowledge of numbers and lettering on the spark plugs.

I have purchased other plugs at this time that are the correct ones but it would still be helpful to know what negative effect if any the L78YC plug would have on the motor operation as compared to the L82 that the motor called for in Champion.
 

alldodge

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Re: Spark plug question for 1987 Mercury 25 hp 2 stroke

Champion makes L82C (spec below) made for performance but has a short life span. Note: the L82YC uses nickel allow copper center and heat range is at 82 instead of 83. Less performance but better heat conduction, bit greater life span

L82C
Thread Size: 14mm
Hex Size: 13/16" (20.6mm)
Reach: 12.7mm (1/2")
Seat Type: Gasket
Heat Range: 82
Terminal Type: Solid
Resistor: No

The L78YC (L82C) is a lower heat range plug and has the same life span as L82C and L82YC respectively.
L78YC
Thread Size: 14mm
Hex Size: 13/16" (20.6mm)
Reach: 12.7mm (1/2")
Seat Type: Gasket
Heat Range: 78
Resistor: No

My guess is the person went to replace them and his parts store didn't have the correct ones so these were used instead. Being colder there would be a bit less in combustion temps which could cause increased deposits but may very little to cause a large problem.
 
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