Carb Problem

[ralphone@domain.elided]

I am having a new problem this month and I'm hoping someone can help. 
My spider has a 2L with euro cams and dellortos.  In the morning the car
runs great but as the engine warms up a flat spot develops between 1500
and 2000 rpms. The car chugs until the tach hits 2000 and then the car
pulls away cleanly?  

I've tried various carb cleaners, different distributor, coil, replaced
the accelerator pump diaphragms and o-rings in the carbs all to no
avail.    

I'm guessing its heat related and the mixture is leaning out in the
transition from idle jets to main jets.  Feels like the accelerator pump
is not working when the engine is hot?   Would any body have any idea
why this would happen?

Thanks in Advance
Ralph DeLauretis
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