I have been told that when you use nitrous you should only run a manual secondary carb to ensure the secondarys open all the way. Is this true ? I thought the plate under the carb metered the fuel amount to ensure proper mixture.
Thanks

YOU CAN RUN IETHER A VACCUM OR MECHANICAL WITH NITROUS. WHEN YOU PUT YOUR FOOT TO THE FLOOR ON A VACCUM SECONDARY CARB AND HIT THE NITROUS AT THE SAME TIME YOUR ENGINE WILL LOOSE ALL VACUM ALL AT ONCE(BECAUSE OF THE NITROUS/FUEL MIX RAPIDLY BURNING IN THE ENGINE)AND THE SECONDARYS WILL BE AUTOMATICALY OPENED DUE TO THE INSTANT DRP IN VACUM. I RAN A 780 CFM VAC. SECONDARY CARB WITH A 200HP CHEATER SYSTEM ON MY CHEVELLE YEARS AGO AND HAD NO PROBLEMS WITH IT.
GOOD LUCK!

Vacuum secondaries do not open due to a lack of vacuum. They open when air velocity through the carb is high enough to pull the diaphram up against the spring. The diaphram is connected to a rod which pulls the secondary linkage up and open.

I cannot say for sure if it matters which type carb is used with N2O or not, but my personal preference would be a mechanical secondary carb.