Any ideas what this can be???? HELP..

Ok i put in a Phenolic spacer...i put in a fuel pressure gauge...also put in a fuel pressure Regulator....And STILL have a stumble and now i actually can see the gauge drop pressure...it does it in 1st and 2nd gear under a load...giving it gas but here is the funny thing it doesnt do it all the time seems like it does it when cold...When its warmed up it might do it a litttle once in a blue moon....I have the pressure set at like 5 ish i bought a cheaper regulator it seems not to adjust very well....I need to buy a better one...But still i see the fuel gauge drop then stumble what could be wrong

Rick James said:

My holley 650 has a slight stumble when its cold,but once it warms up i dont have any problems.I would say its lean down low ,did you set the floats and the idle fuel mixture with a vacuam gauge?5 psi?is that what the edelbrocks are supposed to have?for a holley that would be low,so check with edelbrock.

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I set the idle mixtures screws with a Vac gauge...the carb i never opened up yet so the floats i dont know im guessing there ok....Edelbrock in there directions state 5.5 max 6psi....so i was figuring set it were they suggest....Also i have an Air fuel gauge its actually running rich down low well ever were it idles at 12.5 and runs around 13.0 when floored it goes back to 12.5...its a 650 thunder series ..I really want to get rid of the stumble 1st then i can tune it....