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90hp efi spark plugs

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Jim Allain

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I have a 2011 OR 2012 90hp efi 4 stroke serial #1B95118 The emissions tag says it takes NGK LFR4A-E That is also what I took out of it to replace them however the threads looks like they are running hot and when I type the serial # in it says I have a 2012 motor and it takes KGK LFR5-AIX which is a cooler running plug and available in Iridium. Gap says 32 on the 4A plug and 40 on the LFR5 plug. Investigation shows that Mercury has been known to screw up the stickers on some engines. It was running OK on the LFR4's however one fouled out so I pulled them all and I have the burnt threads on all 4. Any ideas on which way I should go with this? I did not put the ones that I just took out in, it came with them when I bought it used. Also no alarms sounding to indicate any trouble.
 
Mercury Marine discontinued model years about 2006 or 2007. Said they "did it to protect the consumer"
In other words, they had a warehouse full of non-current motors.
Always use what the emissions decal says unless there is a later service bulletin.
 
The portion of threads extending past the cylinder head & into the combustion chamber (typically 1 maybe 2 threads) usually is discolored.
We are getting into some exotic plugs but in the old days heat range was determined by the length of the insulator cone & center electrode.
Perhaps a current Merc guy can look up service bulletins if any.
 
OK Thanks. I had already ordered the 4A's before I uncovered this problem so I'll just put them in when I get them and give it a shot. I just don't want to burn something out.
 
Jim Allain said:
I have a 2011 OR 2012 90hp efi 4 stroke serial #1B95118 The emissions tag says it takes NGK LFR4A-E That is also what I took out of it to replace them however the threads looks like they are running hot and when I type the serial # in it says I have a 2012 motor and it takes KGK LFR5-AIX which is a cooler running plug and available in Iridium. Gap says 32 on the 4A plug and 40 on the LFR5 plug. Investigation shows that Mercury has been known to screw up the stickers on some engines. It was running OK on the LFR4's however one fouled out so I pulled them all and I have the burnt threads on all 4. Any ideas on which way I should go with this? I did not put the ones that I just took out in, it came with them when I bought it used. Also no alarms sounding to indicate any trouble.
Click to expand...
You are missing a digit.
 
Droid said:
Mercury Marine discontinued model years about 2006 or 2007. Said they "did it to protect the consumer"
In other words, they had a warehouse full of non-current motors.
Always use what the emissions decal says unless there is a later service bulletin.
Click to expand...
Mercury did it to follow Yamaha's lead. Which was then followed by all of the other motor makers.

There were not enough significant differences in outboard motor models from one year to the next to have them be model years.

I think that it has been proven that going by engine serial numbers is a much better system. Changes can be made at any time during the year. No need to wait for a following model year.
 
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