It would really help to know which thermoquad you have. There are basically three, the first series was introduced for the Mopar 340 engine these are all 850 CFM, then the Competition Series came along ( all CS thermoquad are 1,000 CFM) and then there is the later or 9000 series thermoquad, The 9000 series were avaliable either as a 750 to 800 CFM identified by the front throttle bore at 1 3/8 inch's and the other is 800 to 850 CFM indentified by the bore size of 1 1/2 inch. All thermoquads have a rear or secondary bore size of 2 1/4 inch. The type and place ment of the choke will also help in telling you which one you have as well. There also was a model # stamped on the lower left rear bolt flange. Some thermoquad also had tags attached to a front screw and some have a Bar Code sticker usually long gone with a model #. Forget the stamping # on the body of the carb they are parts # and could have been changed.

Also you mention you were running a Edelbrock 600. Sense all thermoquad 's are spread bore Carburetor's did you change to a spread bore manifold? Or are you using a spread bore adapter? If so and you "ARE" doing one or the other could that be the problem? Manifold installled correctly? Same for the adapter!

Roland