1999 Suzuki Intruder VS1400 misses and backfires on one cylinder particularly loudly on startup. Gas consumption is high. Some loss of power. Operates best at high speed, poorly at low speed. Condition getting worse. Carburetors have been cleaned. What is the problem? How can I fix it? How much will it cost? How long will it take?

I have problems with a 800cc and I cannot find an adjustment screw I have problems with a 800cc and I cannot find an adjustment screw

There are no external mixture adjusting jets on these carburetors. Idle mixture is set by a fixed internal jet. High speed mixture is adjusted by a moveable jet attached to the throttle slide. As a related aside, there is a small O-ring sealing the needle valve to the carb body. In an older bike the rings become brittle and may let fuel leak past causing flooding of that cylinder. There are no external mixture adjusting jets on these carburetors. Idle mixture is set by a fixed internal jet. High speed mixture is adjusted by a moveable jet attached to the throttle slide. As a related aside, there is a small O-ring sealing the needle valve to the carb body. In an older bike the rings become brittle and may let fuel leak past causing flooding of that cylinder.