What is your fuel system set up? Hose size, fuel pump model, tank and vent set up.
Check that the high speed bleeds are the correct size, are not blocked. Float levels center of glass or bottom of plug when taken out (if you have plugs). What is the list number on the carb, and what size jets now.
Don't think it's fuel supply. I installed a fuel pressure gauge and watched it all the way up and it stayed at 7psi. For the record, it is stock tank with vented cap. Walbro 255 pump regulated down with a Mallory regulator. 1/2" fuel line with 3/8" return.
Float level is to bottom of plug.
List number is 4781-5.
Jets are 78s on the primaries and 84 on the secondaries.
Change spark plugs before you get too far. Donít get too carried away with plug gap.
Start by checking plugs, wires & the rest of the ignition, maybe the valve springs. Misfiring will show as lean.
Could the popping be from valve float?
If ignition or valve float, wouldn't it go rich instead of lean? It is a whole new ignition system with new distributor, wires, and plugs. Retarding the timing did not help.
What are the high speed air bleeds ?
Assuming fuel supply system ok
[pump lines pressure all correct ]
Change secondary high speed air bleed for smaller . This will cause more engine vacuum/suck on jet ie richer mixture
What is the cruise mixture ie on primaries light constant throttle ???
vehicle speed and Engine rpm at cruise ??
The theory about fuel CURVE
fuel mix taken every 500rpm
1/ flat horizontal straight line up and down =main jets
2/fuel flat curve angled either gradually up or gradually down
=low speed bleeds to shift start of diagonal flat curve up/down
=high speed bleeds to shift end of diagonal flat curve up/down
3/primary jets = light throttle cruise 40mph to 55mph
4/ secondary jets = 3/4 throttle
5 / power valve start to engage at 50--55 mph or equivilant engine vacuum ,drill out to provide correct mixtures .at 100% throttle.
If the fuel curve is actually either U or upside down U =emulsion jets
During cruise, it is around 13:1 at about 2700rpm. During accel, it starts rich around 11:1 at 2k rpm. It gradually gets to 14+:1 by 5k rpm.
I'm late but will re-iterate what Bill said, ensure fuel level is correct, as a low level will lean it out top of pull for sure.
my "race" 850 is dumb simple old skool ( no adj bleeds) and works mint.... 77 w/085 PV primary, 80's w/045 in rear.
Same config run on dyno, AFR was perfect thru the pull. Jets wont matter in a assymetrical AFR problem like this.
ALSO, again shirt tailing on Bill, before you pull it apart, blast some carb cleaner down the orifices in the top of the air horn to ensure the air bleeds are clear.
So blast and check float HOT b4 any parts changes, which I dont think you need.
If the air bleeds are restricted, won't that make it run rich?
As a test, can I add a restriction to the high speed air bleeds?