I've had similar issues with old Holley carbs. They don't like to sit. Rebuild kits are like $20 and only take about an hour. Good luck with your ride.
Just rebuilt my dual 780's 2 months ago. Due to a cracked throttle plate on the rear carb. Ordered one from summit and it came machined wrong. The butterfly's would bind and not open all the way. Only about 1/4 throttle. Carbs are fickled lil things. I also run multiple filters. Have one about 6" from carb fuel rail.
