Seeing your black plugs earlier makes me think compression is good enough. . .
IIWM, i'd verify all plug caps, connectors and plugs were getting juice and sparking properly, then ensure carbs setting on 1/4 are similar to 2/3. Check for blockages.
Any chance pilot jets on 1/4 are of a different brand than 2/3? overall length of the pilot jets the same?
Go back and clear tube 1/4 to be sure....