Adding another F to Fast Fuel Flow Faucet

I have three Lambrettas all with 200cc rebuilt engines ,that is new cranks ,bearings ,oil seals top ends and 12 volt conversions etc. All run with distinct but different characteristics leading me to believe the variations are carburettor induced.However mere swapping of the carburettors hasn't necessarily correlated to isolating the differences.
Not wanting to get too involved in the “Black Art “ of carburettor jetting / tuning I have instead tried buying new Jetex carbs supposedly suitable for standard engines,with mixed results.
My GP ,on completion of 380 miles “running in” I decided to push the speed up and over 50 but after a few minutes at high throttle setting suffered loss of power and fearing partial seizure coasted to a slow speed but was surprised when releasing the clutch the engine restarted. With reduced speed I managed to limp home noting that the power fade was now more apparent whenever the throttle was opened to climb gradients.
As a strategy for diagnosing this particular problem and after LCGB forum research I began with investigating fuel flow. I tested the fuel feed rate with a container at the same level as the carb and despite the tap being supposedly rated as“Fast Flow” measured 280 mL (just under ½ pint ) per minute.
A further two (different makes) “Fast Flow” taps were bought both returning similar flow rates.
Being reluctant to modify an existing tap I have been searching for a genuine “Fast Flow” tap that specifies a given flow rate ,which I understand should give approx 1 pint per min. Even the advertised Youtube featured SIP demo (which is in German) https://www.youtube.com/watch?v=DvNHuXfCVGU shows an original, versus SIP fast flow tap discharging into calibrated containers BUT with no reference to time!
Is there a product on sale that clearly states a flow rate ?
Not wanting to get too involved in the “Black Art “ of carburettor jetting / tuning I have instead tried buying new Jetex carbs supposedly suitable for standard engines,with mixed results.
My GP ,on completion of 380 miles “running in” I decided to push the speed up and over 50 but after a few minutes at high throttle setting suffered loss of power and fearing partial seizure coasted to a slow speed but was surprised when releasing the clutch the engine restarted. With reduced speed I managed to limp home noting that the power fade was now more apparent whenever the throttle was opened to climb gradients.
As a strategy for diagnosing this particular problem and after LCGB forum research I began with investigating fuel flow. I tested the fuel feed rate with a container at the same level as the carb and despite the tap being supposedly rated as“Fast Flow” measured 280 mL (just under ½ pint ) per minute.
A further two (different makes) “Fast Flow” taps were bought both returning similar flow rates.
Being reluctant to modify an existing tap I have been searching for a genuine “Fast Flow” tap that specifies a given flow rate ,which I understand should give approx 1 pint per min. Even the advertised Youtube featured SIP demo (which is in German) https://www.youtube.com/watch?v=DvNHuXfCVGU shows an original, versus SIP fast flow tap discharging into calibrated containers BUT with no reference to time!
Is there a product on sale that clearly states a flow rate ?