I think that the problem is clearly related to vacuum leaks. If
the suggested procedure with the vacuum hoses yeilded no results, you
should then look for vacuum leaks. This is indicated both by the high idle,
and the fact that the engine will run with your hand covering the air cleaner
intake (if I understood you correctly).
To find vacuum leaks, you can run the engine and spray starter fluid
near where all the joins are; intake to head, carbs to intake, and misc
vacuum fittings. don't forget the EGR valve too. Alternatively, you can
just go ahead and pull off the carbs and intake and reseal them. I recommend
Permatex Ultra Copper; it's worked better for me than the original gaskets.
This should take care of most of your problems. Of course, you will now
have to go through and re-tune your carbs. Also, make sure to check the
timing before you start tuning, as this will affect all of the settings.
Good Luck!
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