Hope everyone is doing well. I need help, in more ways then one, lol. I am just finishing a total build on my XS2 and am having an issue I have never had in owning and working on these bikes since 71. Bike has all new ignition, dwell set to spec, timing on spec, advance on spec. Charging system is perfect , new battery and all wiring connection triple checked for proper continuity. Carbs have been ultra sonic cleaned multiple times, all passages blown out with air multiple times, petcocks rebuilt , new fuel hoses with filters. Both carbs have new kits installed , floats tested and set to spec , choke enricher plunger replaced and tested for proper operation with air. Bike starts ok, warms up ok , produces great power from start to full red line. I have checked the carbs air flow with a meter that I use to balance carbs. Now the issue. The LH side blows white smoke, the RH side is always clean. I have tested the cylinder head temp and exhaust temp on both sides to make sure they are very close to the same. I have tested the exhaust output with a CO meter and the LH side is defiantly running rich. I have reset the LH carb float anywhere from 23 mm to 27 mm with no difference. The pilot jet and main jet are stock size, the needle is set on the number 2 highest ring, both diaphragms work properly when compared. I read where someone said it might be valve seals, so I swapped the carbs over side to side complete with throttle cables and the problem switched from LH to RH which only verifies in my mind that it's not the valve seals, it's the carb . I am lost and going in circles, as I can't fault anything in the carb that I can see. I am in DESPERATE need of help !!