Originally Posted by shaddix
Hey guys! I looked at my spark plugs today and they were black. So going by this guide
it says to run it at full throttle and check to see if they're black or white or tan as a first step to determining jetting needs. Now considering that my plugs are already black, will that mean that if it's too lean at full throttle they won't be white? Do I need to clean the plugs first before I test for lean/rich mixture?
How old is your bike and how many miles? What's your gas mileage, has it gotten worse? If you've had the bike for a while the jetting may be fine. The two o-rings in the carb may be failing causing a rich mixture at all throttle settings. We spend most of our time on the needle circuit, so this would be the one start with. Since the USA bikes don't have an adjustable needle, you can't drop the needle one clip. This means that I'd check the needle for wear (smaller diameter would flow more gas) and check the needle jet for 'ovaling', another wear point on some bikes (larger hole, more fuel).