Before I would do anything, I would squirt something like Marvel Mystery oil into the cylinder and let it work for about a week. You may well have an intake valve full of varnish and the oil will dissolve it. You can loosen the the valve adjustment and move the rocker to the side and pull the pushrod, but you have to be careful. Sometimes the pushrod sticks to the lifter and pulls it out of the hole. Then you have to take the side cover off. If you turn the engine to where there is clearance on the valve, you can spin the pushrod and look down in the hole with a light and see if it is bent
