Hey Crosbyman – Marineengine.com lists the Champion plug for a 1974 9.9 as UL-81C, not L82C, but I’ve seen disagreement before as to where you go to look spark plug usage up so I’m not too surprised you have a different number. . They list the L82C for 1977 and newer. – probably a wider gap plug for the higher energy spark.

For the problem motor I fixed with NGKs , I used BR7HS plugs to cure it, which is the UL-81C equivalent,

Marine engine’s usage chart below : https://www.marineengine.com/parts/champion/outboard/johnson-outboard-spark-plug-guide.html

Dave

• This reply was modified 2 years, 9 months ago by outbdnut2.
• This reply was modified 2 years, 9 months ago by outbdnut2.

OK, well I remember the recommended champions years ago being the UL-81J gapped at .030″. I think the are now referred to as UL-81Cs though… Marineengine seems to contradict itself just a bit though, they refer to L-82C plugs, then go on to talk about L-86C plugs… Just looked at the BRP site, 74 plugs seem never to have been update from the originals….Then looked at 76 models, where they referred to the UL-81J plugs… Don’t know if Champion still makes the UL-81Js, probably referred to as UL-81Cs is still produced… Just looked on the Champion site, which is pretty tough to navigate, they spoke of QL 82C/L82C also. But, it looks like the UL-81Cs are available also….
Don’t know what to say about the L-86C recommendation, probably for extended trolling only….