Triumph Repair: Spitfire Zenith Carb Mixture adjustment, zenith carb, jet adjustment

Question
Hi Howard,

Thanks for your previous response ref carbs and interchangeability. I have the SPitfire 1300 running on the Zenith single carb now...but very rich ...plugs are black and sooty. How do I adjust the mixture to go leaner?..I've googled this to death but cant find relevant diagrams or references. The is a large WHite plastic hex nut with an adjuster screw in it to the right hand side...looking at the engine ..of the carb body...is that it ?

Thanks

Steve  

Answer
Hi Steve,
The jet adjustment is down in the top pot under the cap with the pin and piston in the oil. It is a 3mm Allen screw. A few were plugged so you couldn't change it. More often when you have a over rich mixture it is a choke failure not a jet adjustment.
The white knob is a trimmer adjustment and usually can't make it run so rich as to flat blacken the plugs.
Howard