Carb Woes

[His Dudeness]

Here's a guess. Was the bank of carbs ever split? There's springs and linkages that join each carb to the one beside it. If the carbs were split and a spring was left out or the linkages weren't put together correctly the adjusting screw that you're turning might not reach. If I was you I'd identify which cylinder is having the problem and then try and get a look in at the linkage between that carb and the one beside it. Does it look correct? Is there a spring missing? Are the linkages lined up properly? See the little springs in the picture. There's one above and one below