Low end torque missing?

Hi All:

Any help on this issue?  I've got a new build (150 Super 3-port) and seem to have rather poor low end torque.

New build includes:

-SI 24/24e carburetor with 160/BE3/115 main jet and 55/160 idle jet

-Mazzucchelli crank with modified inlet timing only

-DR 177 top end kit

-SIP Road 2 exhaust

-Timing at 20deg BTDC

I'm tending to think I have a problem with the mixture as it seems to be rather sensitive to the presence of the air filter.  Air filter off is worse than air filter on.

Any suggestions would be greatly appreciated!