Choosing the right carb for my car (340 4-speed)

crackedback said

Timing first! Get that sorted out as MANY carb problems aren't really carb issues.

A 750 vac secondary is like having a 375 2 brl. Hesitations can come from lots of places, too light secondary spring, poor accel pump/squirter combo, too low PV rating.

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I definitely need to address timing since I've done it solely by listening and smelling so far, but the plugs have a perfect burnt marshmallow color and I've absolutely never had it backfire. I will be installing a Rev-n-ator soon and will be playing with the timing then.

I'm mostly wondering if I should return the 600DP and upgrade to the 650DP, or if I won't really notice any gains.

I'm inclined to keep the mechanical secondaries since I have minimal vacuum and a 4-speed. I've heard this is a good combination for mechanical secondaries.