650cfm QFT Carb Tuning / 383 / 727

Nico,
Too much depends on the air bleed configuration to give a simple answer to a simple question.

I'll answer two ways.
If the only problem is 0 to WOT, then the problem is entirely in the idle set up and accelerator pump. If it still does this with secondaries disconnected, then its all in the primary side. That's a huge squirter for the situation. Try a quicker acting pump cam and smaller squirter. Make sure the cam moves the pump arm as soon as the throttle moves.

It's probably not the only issue, so here's in general how I suggest performance tuning.
1. Check Fuel level in bowls. Use the QF recommended starting level.
2. Timing. Timing has to be close to what the engine wants or the fuel mixtures can't be properly tuned.
With the cam you posted, initial timing probably should be around 16 to 19*, 700 - 800 rpm. Do a search for timing curves. I've posted a lot of stuff recently.
3. Adjust the carb's idle setting so the amount of transfer slot visible underneath the primary plates is between .020 and .040" (roughly square). The first time you do this, it has to be done with the carb off of the engine. Take notes on how many turns of the screw is required and you won't have to remove it again for this purpose. I'd start with .040" and as the engine warms up you can reduce it a little.
4. Engine fully warmed up, adjust the idle mixture. Set for highest vacuum or rpm when shifted into D.

Test and tune for steady conditions:
Off idle & Low speed cruise. Slowly open throttle (driving if you can) from stop. If there is hesitation, the idle circuit will need adjusting.
It should get leaner as the throttle opens.

High speed - steady: Driving steady at 60 - 70 mph. This is adjusted with the primary main jets. Just go for good driving for now. Later you can go as lean as it will tolerate and get better economy and part throttle accleration.

Then work on the accelerator pump circuit if it hesitates.

Test Wide open throttle acceleration. You can adjust the AFR with the main jets. But if you later find a big difference between best high speed steady and best WOT power, that can be addressed.

Then work on part throttle power. If there's big hesitation around 2/3 throttle, try an earlier opening power valve, an 8.5 or a 10.5

If you want to get deeper into it, or continue to have problems, then you may want to take the carb apart and check everything. You'll need pin gages or micro-drills to check all of the holes.
QC at these companies sometimes isn't what it ought to be.
See here for example: Q-850 metering block

And if you're going that far, you can get help coverting it to be setup like an old school Holley 650 double pumper. But without knowing the air-fuel correction bleeds of your QF carb I hesitate to recommend copying the jetting of a Holley list 4777 or similar. That said, a 62 is pretty small primary jet for that size carb.*

As far as AFR goes, please read this: Wideband

The AFR meter is nice tool to help understand changes, but tune for performance. By that I mean things like power at idle (represented by vacuum in Drive), economy on the road, and max power by best speed in a 1/4 mile run or Hp on the dyno.

*another factor in jet size will be the booster. Some QF carbs use annular, many use downleg, etc.