XJ650 Fouling Plugs

1980 XJ650 fouling two plugs. Carbs have been rebuilt, synchronized and floats adjusted. I cleaned but did not replace the main fuel jets when rebuilding carbs. Valves have also been adjusted. Runs good except that on 2 of the 4 cylinders plugs keep getting fouled after running for short time. Puts out a lot of fumes when idling. Thought maybe pilot screws on those 2 cylinders were out too far so kept adjusting them to the point where engine won't start. Beginning to wonder if main fuel jets in those two carbs may be wrong size. Either that or possibly the float needle not seating properly. Any ideas?

 

Check the fuel levels in those bowls and see if they are set properly....if the fuel levels are too high, those carbs will run rich. Next possible choice would be choke plungers that are not fully seated on those carbs, holding the choke slightly "open" all the time on those carbs.

Of course, it could just be worn-out plugs on those cylinders, try swapping plugs and see if the problem "follows the plugs" or not...........