I had a similar issue once. It turned out that one of the throttle shaft seals had fallen out. I bought these ones from ebay https://www.ebay.com/itm/2X-Honda-C...ash=item2cb9b18f90:g:0dgAAOSw9GhYkoHD&vxp=mtrhello,
I have same issue but with right side.
I manged to fix all my issues and bike was running like thunder.
But than somehow after few miles or higher rpm ( i dunno why) bike desided to use only one cylinder. So I checked all cables and so on and i managed to get it run good again. everything was fine than again after while just one cylinder.
carbs cleaned million times
and bike is running only on one cylinder Only left side.
I removed right plug and bike was able to start on one left cylinder, but I removed left plug and bike was not able to start. thats mean left side is ok but right side is not ok
I tried to change coils, cleaned carbs, change plugs, sparkplugs, and always its only left side.
i noticed left sparkplug is looking nice yellowish but right side has some oil on spark plug..
so i really dunno whats going on now. i was happy it was everything working but nah its never ending story...
any suggestion guys what may be wrong?