This is completely wrong. Backpressure isn't needed. Freeing up the exhaust simply leans out the mixture on the carbs... and they are already on the lean side from the factory. That's the only reason straight pipes/deleting the 'goats belly' will lose power if swapped with no jet changes. The FIRST thing most people do with dirt bikes (easier to work on) is to free up the exhaust and jet up the carb. Nice seat of the pants difference in power. People also do it with street bikes when switching to free flowing exhausts, as it puts the bike in an extremely lean condition.Highly unlikely that you'll need to rejet BECAUSE of a lack of back pressure. The air/fuel ratio remains virtually unchanged due to any increase/decrease in scavenging due only to minor exhaust changes such as baffles except at the very top end of the rpm scale. If you run the bike at over 7500 rpms for an hour or so it's gonna get hot and eventually burn the exhaust valves. However, the VN750 does benefit power-wise from CORRECT tuning, which involves more than just seat-of-the-pants feel or generalized guessing by reading spark plug colors. An exhaust gas analyzer is needed at the very least, and a dyno always proves fact from fiction. That being said, the Keihin CVK seems a little lean from the factory as a compromise to CAFE standards and a bump up in jets is commonplace. But you're not going to do the bike any harm by just running stock jets without exhaust baffles. Now for all the kids that like loud toys and remove the tuned chamber (goat's belly), removing that item saves a few pounds and immediately loses 4-5 Hp and an equal amount of midrange torque. But you seem to be going in the correct direction, so Kudos to you.