I was working with a 427" SBC that bucked and surged and you could not take off from a stop without that happening no matter how you slipped the clutch.
I messed with it for 3 days trying every tune and jet combo and timing curve. It still bucked.
I noticed a hint of sweet smell from the exhaust and mentioned it to the customer.
He said he got the car at an auction and it had race fuel in it and he had just been using 91 octane pump gas.
Off to the race fuel shop i went and got 5 gallons of 112 octane.
Drained the fuel cell and poured in the good stuff.
No more bucking and surging. It ran as smooth as a new car after that.
Fix your Too much timing issue and see if that fixes it.
Depending on a lot of things your compression and cam choice will not run like another of the same compression and cam.
Surface finish, chamber shape, port shape, the list goes on and on.
If you are running 200+ degree coolant temps try to get them down 180--195 and see if that helps.
I built an 11:1 396" with 23[email protected]
.050 cam 108LSA it has 210 psi cranking pressure and no bad manners at all.
I ported the heads roughed up the runners and all sharp edges in combustion space have been smoothed.
It runs 91 octane with 22 initial and 38 total timing 180-185 coolant temps. 4200 lb truck.
That does not mean your build will like that timing though.
If you feel it is carburetor related then add some jet to it or twist the idle mix screws out some more.
If you back off the throttle all the way you should be in the idle circuit.
Easy enough to try.. I would turn them out 1/2 turn each and retest then 1 more turn each.
Usually 3 turns out from fully seated is a good spot to start from.