912UL Carb sync

Hi,

I am trying to get my carbs synced & having issues. I replaced the diaphrams in both carbs. Went through & made sure the jets matched on both carbs & that the needle clips were in the same position. 

With the carbs on the engine I set both idle screws to the same position & also set & checked the throttle cables start opening at the same exact time. I also checked that the mixture screws were both set at 1.5 turns out. 

With the air filters off & the engine running, as the throttle is slowly increase I can clearly see 1 slide opening before the other. 

Is the fix as simple as adjusting the slow opening side more on the throttle cable adjustment? 

I would think that if the throttle levers on the carbs start moving at the same exact time then the vacuums would be identical........ 

I also held the slides open (engine off) & verified that the butterfly valves move at the exact same time when advancing the throttle. 

Any suggestions......? 

Note: I can't do an intake/vacuum balance of the carbs without some fabrication on the crossover tube. The crossover tube was modified by the previous owner & is now a 1" tube with only 1 sync port on the right bank. There is no port on the left bank for hooking up vacuum gauges. 

Thanks,

Jesse