Is my 340 Overcarbed? Avg 5-6 MPG

Holleys can be such a pain to tune--yeah they do make more HP then any single Carter carb. If your not looking for best HP, I would think about a 600 Carter Competition carb. The metering rods are easier to change to tune it and it will likely idle better to boot. Flame away, lol, I ran holleys for over 20 years and yes they can be the best carb out there but my dual Carters give me less fuss then any Holley-Demon carb I had...I'm sure one Carter would work just as well, just be down on HP.

Thats just my 2 cents, if you want another Holley, go for it..just make sure the metering block gasket doesn't have an internal leak that causes a rough idle--that was the last straw with my Holley days, freaken thing would be OK sometimes and then not OK after a jet change--even using a new gasket sometimes.

Then you might need to adjust the idle feed restricters or idle air bleeds to get the best idle...I had pin drills, mics, all that stuff and had had Holleys run great all season. It can be done, I just think a Carter carb would be easier to get running around town if max HP isn't needed. It idle better and get better MPG with less tuning