I took a look inside the valve covers and did not see any obvious problems. No broken springs. The engine is compressing fuel back up through the carb. It is on a rhythm like only one cylinder. All is good at idle till you advance the throttle or put a load on the engine. It acts like the intake valve is not closing and the compression stroke is pushing the fuel/air mix back out the intake and up the carb.
I will do a compression check next to see which cylinder it is. I am not looking forward to taking the head off again. I hope this can be an easy fix.
Chris