The Kymco Yager GT 200i manual states that the following spark plug is to be used:
NGK DPR6EA-9 (standard)
NGK makes an iridium plug that will work for our scooter, but it's one heat range cooler than our OEM plugs:
NGK DPR7Eix-9 (iridium)
You can get these plugs from Kragen/OReilly auto parts (although they're not usually in stock. I had to get two of them shipped to my nearest store from another store).
According to Denso (another spark plug manufacturer), a good cross-reference plug is:
X20EPR-U9 (standard)
Or, for an iridium plug from Denso, it is also one heat range cooler than our OEM plugs:
IX22B (iridium)
The heat range of a spark plug determines how well it will survive in the environment inside the cylinder. Too hot, and you get melting, blistering and breakage of the spark plug metal and ceramic.
Too cold, and you get fouling of the plug.
Personally, if I couldn't find the exact right heat range plug, I'd rather go with the next colder range than the next hotter range.
I believe the NGK iridium plug would be a good fit for our scooters, despite the fact that it's one heat range cooler. The iridium plugs are very resistant to fouling, and our fuel-injected Yagers simply don't foul plugs like a carbureted engine does, because the fuel metering is more precise (i.e.: when you crank open the throttle on a carbureted bike, the cylinder gets a dose of rich fuel/air mix from the accelerator pump or power jet (which is often poorly tuned on small carburetors and just dumps a lot of fuel into the intake during rapid throttle opening to prevent lean-out bogging) until the engine gets up to speed and the air intake velocity can draw fuel from the float bowl, which can lead to earlier plug fouling).
The thing that really causes the most plug fouling is running the engine at a low RPM for long periods of time. But because we're running a CVT, the engine speed is nearly always high (I was riding at 12 MPH today in a parking lot, and my RPM was 4000!), so that's another reason that a plug one heat range cooler than stock should be OK. If you need to clean the plug, it can usually be cleaned up pretty well by taking the scooter on a long, high-speed run to get the plug up to its self-cleaning temperature so that it can burn off the carbon deposits.
Again, having to ride fast for a while because you're using a plug that's one heat range cooler than stock is a lot better than finding chunks of melted spark plug metal or chunks of broken spark plug ceramic in your cylinder because you're running a spark plug that's too hot.
Another thing that tells me that running a spark plug that is one heat range cooler than the manual specifies is that the carbureted Dink 200 service manual specifies a NGK DP7EA9 spark plug, which is the same heat range of the Iridium plugs I've got.
