carb gaskets aren't usually the problem, unless it's the intake gaskets, but even those will just lean it out unless they're real bad
could be bad crankcase pressure, you're only measuing topend cylinder pressure. Could be timing but that doesn't usually go out on it's own. still worth a check
have you tried running it straight off starter fluid? don't do it for any prolonged times, but it's great for diagnosis.
read thru this: http://www.mopedarmy.com/wiki/Fred's_Guide