[Tigers] Vapor lock/fuel percolation

[awtiger]

Guys:

After all the stuff I've done to the Tiger ignition-wise to get it to quit 
stalling, I'm finding myself starting to consider other possibilities, such 
as vapor lock and fuel percolation.  To make a long story short, the car is 
leaving me on the side of the road when it's up to operating temp and warm 
outside.  It caughs and sputters and won't take any throttle at all at low 
rpm.  When I coast off to the side of the road and take off the air cleaner, 
I'm seeing what I would consider to be a large amount of vapor coming from 
the overflow tube (Holley 465 4 bbl).  It also periodically spits fuel from 
the center squirter down the throat of the carb.  From what I've read on the 
'Net, this sounds like a classic case of fuel percolation.  One other 
thing...the car will always start back up and run, but will not take any 
throttle or any low rpm load.  Also, when I manually open the throttle, I am 
rewarded with fuel squirts (at least I know it's got fuel in the carb at 
that point).

What I can't figure out is, if it is percolation, what has changed to make 
it do that?  I've made no changes to the fuel system of the car.  In fact, 
until the recent ignition tune-up, I'd made no changes to the car for many, 
many years.  It's never done this before.  The car is also running at the 
same temp it's always run at.  Could the gas we're getting nowadays be 
responsible for this?  I always run 91-octane premium (real gas, no ethanol) 
and have for years.  I've heard there is such a thing as "winter mix gas" 
and "summer mix gas" and that each have a different temperature at which 
they volatize.  Due to some serious drains on my time lately, the last time 
I filled the car up with fuel was in May.  Could I just simply have a load 
of "winter gas" that volatizes at a lower temperature?

Any suggestions???  Please somebody send me to school here...I'm beginning 
to feel really stupid.

Andy Walker
Edmond, OK
B382001600LRXFE
TAC #740