i have some tripple webber carbs on my new 73 240, and I was just wondering how much horsepower they add.

not much unless you do something to you cams

opps sorry missread your post, done correctly, bored out with the correct cams about 30% - 35% I think

A carb change (or any part change) by itself may improve or may even degrade performance. The engine systems all opperate as a unit so it really depends on the supporting pieces.

What model/size weber carbs do you have, what modifications have been done to your cylinder head and/or block, exhaust, or ignition?

When all else fails put it on a chassis dyno! There is a shop near me that just started offering three pulls on the dyno for $50!

Rocye, which shop is that, and do they offer WBO2?

I know of about 2 or maybe 3 in the Sac area, but used a place in San Jose last time, for $100 an hour.