Been through all of the hoses & replaced the PCV valve. Pulled each hose one at a time & capped the barb at the carb. Closed the choke slowly, no increase in idle until it died. Finally, emptied a can of carb cleaner all over everything; no change. Motor actually idles well and even, as noted there's no sucking from the tailpipe (well, once in a blue moon...might be a slack timing chain). Checking the plate in a bit.
