Erradic loss of power (again)

[Joel Sell <jsell@xxxxxxxxxxxxxxx>]

Volks,
	I posted this question a few weeks ago and got some great
responses. I have gone through them all, but so far NOTHING has
worked.
Here's the problem:
	'73 bus with the 1700 pancake engine, webber progressive
carb.  Sat in a garage for 8 years until the owners asked me to get
it running. Everything works great now, except for a sporadic power
loss. The engine will idle, but has no power whatsoever to get the
bus moving. There seems to be no warning that the power loss will
happen, and there seems to be no method to it. Sometimes it happens
when the bus is sitting at a stoplight, other times it happens when
the bus is driving. Some days there is no power loss at all, and the
next day it happens three times! Then the next day it happens once.
The only thing that is consistant is that the engine is always warmed
up when it happens, and after I replace or clean something, the bus
runs great. Then I give it to the owners and they call me the next
day and tell me it's happened again.
Here's what I have done:
	Changed Coil
	Changed Condenser
	Checked fuel lines for blocks
	Checked fuel tank for blocks
	Cleaned out and rebuilt carb

Any more suggestions?

Thanks,
Joel  74'  Westy