At the risk of giving you too much information.......
I have been living this quandry for awhile now but have hit the sweet spot finally.
Here is what I have learned.
First you do need to adjust the carb after installing the sidepipes. Beacuse of the reduced back pressure your engine is now a more efficient air pump.
Second, you do not "need" backpressure. The less backpressure you have the better. To maximize the benefits of the lower backpressure you may have to make other modifications though.
I have the same sidepipes. I started with the "reverse-flow" muffler inserts (open pipes were just asking for police attention which I really don't need). These were a mistake, they suck or should I say cork. By going to the "glasspack" inserts I gained at least 100 hp and 1500 rpm ( be sure to install them backwards to realize the greatest flow). They sound great.
I spoke to another gentleman on this site and he mentioned that his buddy rigged up an even a less restrictive baffle system.
Anyway back to your specific question regarding carb adjustments.
My first recommended change is to purchase an edelbrock (or similar) air/fuel monitor. They aren't too expensive, under $150, and if you bought the sidepipes you can certainly afford it
. It is a GREAT tuning aid. I welded the oxygen sensor bung on the drivers side pipe just after all the header pipes meet in the collector. It sits horizontal to the ground just under the frame rail.
The guage fits very nicely in the air conditioning duct which is covered by the "Corvette" plate in those cars like mine which don't have A/C (yet..Vintage Air on it's way with Chris' help). You can use the other side for a Knock Sensor guage or fabricate a cover plate. With or without it you probably need to go richer in the mixture. (More air requires more gas). You may just be able to richen the idle circuit, all carb systems contribute to the overall fuel delivery.
Hook up a vacum guage and adjust the idle mixture to maximize your vacum. See how it runs. If it still bogs try a little richer, if it that doesn't help reset the mixture to the highest vacum and then go a little leaner until the vacum just starts to fall.
Next step is to play with your primary circuit. This procedure of course varies with the carb. My experience is limited to carter/weber/edelbrock and fuel injection systems. If you have any of these system e-mail me and I'll give you the procedure. If you have a Holley or Quadrajet there are many good manuals out there. It's time well spent.
The other change that you should make is your timing. Generally you need more advance faster with a less restrictive exhaust. I would recommend going with one step lighter springs in your distributor. Adjust your initial advance so that (with your vacum advance disconnected) you get 36 degrees of advance at 3000 rpm. Just hook up your timing light hold the rpm at 3000 and turn your distributor so it hits the 36 degree mark.
This is not a final setting of course, every engine is different, but is a good starting point.
Have fun!
