Remove the check ball and try it again. The vacuum can is holding air and keeping it open. I have ran 3310 and 1850 holleys without the check ball and never had a problem. kwik check on if it is the check ball is remove carb hit the throttle linkage to wot and if it sticks turn it upside down to unseat the ball. If it then closes you found the problem. Then go back to remove the check ball.