I have a billit metering block with the screw-in restrictions. I used it to tune may carb, then used that as a guide for modifying the stock metering block.
This was after making all the standard tuning adjustments.

I tried the larger squirters with limited success. To start, jet that puppy bigger 2 to 4 sizes per jet (primary and secondary) if the problem gets less, you need more fuel from the accelerator pumps. I believe the 650 comes with 31 nozzles standard. Going bigger doesn't help as the 30 cc pumps don't have enough volume per stroke to spray the fuel in as it is needed. I put dual 50 cc pumps on mine with 31 nozzles and I used the brown pump cam, turned it so it was about to push the accelerator pump lever, marked it and drilled my own hole. Hesitation went away for me.
You need more fuel, the manifold is fairly big for that combo, it has no exhaust crossover to heat anything so it needs more fuel.
This is all assuming the engine is happy and the carb is as well.

I ran a 650 double pumper on a .040 over 360 in my 4x4 in 80`s,it had 12-1 jahns pistons,strip dominator manifold,13/4 headers,2.02 int valves.First thing I thought was maybe a little over carbed on 318.But reading thru replys they are good with fix tips.Mine was 75 white sweptline express with keystones and 12/33 15 tires.Twisted yokes on transfer case pulling wrecker and mobile home out of mud with both burried.I did not lack for power.....lol

The 650dp comes with 28 squirters F&R.

having been down this road before putting a hirise dual plane and vac secondary 600 on a previous stock 2bbl with 2.76 gear.
It killed the off idle and bottom end.

assuming the carb is ok..my cure was alot of time experimenting on initial timing the idle mixture and timing curve. getting a clean idle with alot of initial and lighter spring for quicker advance was the fix but you have to deal with pump gas and pinging issues also if your to agressive.

need to limit total advance also since alot of initial and the lite springs will put total to high.

more gear would help if you are running "hiway" gears now.

Havnt had a chance to work on the truck for a while but I found out that the miss and hesitation up top was from when I found out that I forgot to hook up the vacuum advance back up and then after hooking it up I checked the timing again and the total was at 52 degrees. Guess Ill have to lower the initial a little to get it back down.