Large rpm drop
Since it came up earlier, here's a graphic of 'idle' system vs. main system.
Idle is in quotes because the Holley 'idle' system really is a low throttle position system. It's not just idle so the name is deceiving.
The lower pressure (vacuum) under the throttle at the transfer and idle port is what moves the fuel.
The mains start when the air velocity through the boosters creates a low pressure zone.
The idle and transfer lot may continue to be subject to low pressure and contribute some fuel, or as throttle opens further, they may not.
My experience has been the mains fully take over under steady state cruising somewhere around 65 mph, 3000 rpm.
Since it came up earlier, here's a graphic of 'idle' system vs. main system.
Idle is in quotes because the Holley 'idle' system really is a low throttle position system. It's not just idle so the name is deceiving.
The lower pressure (vacuum) under the throttle at the transfer and idle port is what moves the fuel.
The mains start when the air velocity through the boosters creates a low pressure zone.
The idle and transfer lot may continue to be subject to low pressure and contribute some fuel, or as throttle opens further, they may not.
My experience has been the mains fully take over under steady state cruising somewhere around 65 mph, 3000 rpm.