Someone tapped the head on this 1980 CM200t 6v and only one side uses the standard 10mm plug. The other side has a 12mm large bore plug. Can anyone help find out what plug will work in this bike on that side? I have it running, but need to replace the plugs. The 10mm side is the correct c7hs.
Does the length (reach) match the standard plug? Have you ridden the bike enough to get a valid color reading on the plugs? If it's running well and that plug is the desirable tan color you're probably OK replacing it with the same thing.
That's not likely a spark plug problem. Most important to ensure the reach is correct so the spark is occurring in the proper location (and the piston isn't hitting the plug). A good tuneup and possibly some carb work should get it running. Some of the folks here with more expertise on spark plugs might be able to better advise you on selection.
Strip them carbs off and make sure all the jets are clean. Make sure they are stock. Depending on air filter and pipe they may be bigger than stock. Don't get too crazy just get some different guage wire and poke the holes. They get gunked up. Lol. Dirty.
You would be suprised on what previous owners do to jets. It is not understood by many. Could be way off could just need a few adjustments.
Jetsrus.com has everything you need.
Spray the orrafices with carb cleaner and air if you have it. Them slap then back on. New fuel, new plugs.
If you don't have full throttle response then start looking into the electrical. It may hesitate and what not but you should get to high rpms if the mains are even close.
Regarding the plugs, I did the same thing to my 84 XL100S. NGK makes a D6HS, its a little colder plug but has the 12mm thread you are looking for and the same reach as the C7HS. You should be able to get a C6HS to match the other side. Hope it helps.
Ok..,I recognize this issue...
I caught it on a old Triumph... apparently what you have is at one point the plug threads in this head had been damaged (crossthreaded or stripped). A previous owner's repair was to tap and install helicoil type thread repair, not an issue. What I see (and had happen) was when these were installed, one may not have "seated" or been sealed properly and what a spark plug was removed the thread came out with the plug.. and possibly discarded without knowledge...
I would install another "repair" thread on the "larger" 12mm hole (correctly) and use the proper plugs for both sides.
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