I see. You'll likely need to take that cover off one more time. You have to look down the holes that the pushrods go into. At the bottom of those holes there is a little dish that those pushrods are made to go down into. They have to be seated properly. If the push rods are sitting on the edge of that dish (the intake valve for example), what happens is the intake valve is held open too much and it will blow back out the carb as you described.
The correct way to do it is to loosen the locknuts up on the rocker arms, seat the push rods properly, and set the gap (lash) between the top of the valve and the bottom of the rocker arm to .002 to .003 inches. You do that while the cam lobe is down (i.e. it is not trying to push the valve open).
You'll have to slowly turn it over and watch the pushrod come up and then go compeltely back down and then make the lash adjustment.
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