Flat Spot / Hesitation

[JMF]

Recently picked up a 70 Charger 383 and just going through some jobs that need sorting

When accelerating or even just at idle at about half way down on the pedal there's a slight flat spot/hesitation and slight backfire through the exhaust , it idles pretty smooth and cruises along ok but the flat spot occurs at that same point when you try and give it some acceleration , it does smell a bit fuely

Checked the timing and seems correct

My setup is pretty stock except a Holley carb

Going to get it on a gas analyser when I can to see if the mixture is correct

Any other ideas ?

Thanks for any help

[XH29N0G]

I'll ask some questions first because

• I would want to make sure the ignition is in good shape and has been checked out before working with the carburetor.  I would also want to make sure the timing was set up nicely because that can also change how the carburetor behaves.
• I would check things like float levels and how the accelerator pump functions first.  the accelerator pump circuit if (1) it does not squirt gas in fast enough (it should squirt as soon as the throttle moves).  This is fixed by adjusting the cam.  (2) It could reflect something with the pump itself it the pump diaphragm is damaged. (3) It could also be that you need a different color accelerator pump cam or possibly a different orifice size on the nozzle.
• If you can find out from the previous owner whether this is something new, or how this started, that might also help.
• I think backfire through the exhaust can point to something other than carburetor.  Backfire through the carburetor can point to a lean condition (not enough gas) for the carburetor.

Now for some more general thoughts about the carburetor.  You said Holley carburetor.  Can you provide more details on the carburetor?  What it is and do you know if it is set up as it was in the box, or if someone has changed anything with it.  Finally, it is possible, if this carburetor wasn't set up properly that your condition might be exacerbated because it might  not getting enough gas from main circuit (jets).  I would hold off on that until later.