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I only ever use plug readings for finding the correct main jet. So I run the motor on full throttle for a substantial distence. If I had one plug which looked as rich as that I would suspect either a leaking valve (low compression) or a carburetor which is affected by vibration (fuel frothing). I set both of my carbs to be identical. When I set the idle, and when I set the needle position, I do both in the same way - I induce the cough by leaning off, then enrich slightly. My main jets are usually slightly too rich, so when I give the bike a real blast, I do not burn valves or pistons.If you read LAB's document on Amal carbs, it says most of our riding is done using less than one-third throttle. If you burned a valve while doing that, you motor would have been coughing and spluttering for miles.
I only ever use plug readings for finding the correct main jet. So I run the motor on full throttle for a substantial distence. If I had one plug which looked as rich as that I would suspect either a leaking valve (low compression) or a carburetor which is affected by vibration (fuel frothing). I set both of my carbs to be identical. When I set the idle, and when I set the needle position, I do both in the same way - I induce the cough by leaning off, then enrich slightly. My main jets are usually slightly too rich, so when I give the bike a real blast, I do not burn valves or pistons.
If you read LAB's document on Amal carbs, it says most of our riding is done using less than one-third throttle. If you burned a valve while doing that, you motor would have been coughing and spluttering for miles.