Installed newly rebuilt Aisin carb from Cruiserparts.net. Old carb was was ok but had a broken screw on the choke valve. It ran, but had trouble starting so we replaced the carb. Now it starts fine, idles fine, accelerates fine, but will not run at 'cruise' speeds. At mid throttle it sputters and blubbers unless the choke is pulled halfway out. Have had the whole intake manifold off, new brake booster, bypassed all smog emissions, thoroughly checked but...I find no vacuum leaks whatsoever. Help???