The damper is a "transitional" device to temporarily slow the rise of the piston when there is a rapid increase in the air speed through the venturi. This has the effect of richening up the mixture for a short period of time. The damper does nothing to affect the piston position during steady state conditions. If you're already running lean on transition, then running without a damper will only make that worse.
@RS02 , You've got so much stuff going on that I find it hard to get a "baseline" from which to operate.
I don't know anything about "Rebello modified" carbs, but my (non-expert) suspicion is if they bored out the throat and changed the venturi area, it will have the effect of leaning out the mixture at the same airflow. So unless you're pulling in more air to make use of the new larger venturi area, then things are not going to work out well. A thinner needle may help mitigate that situation, but I wonder if those carbs were more intended for flat out WOT (track) performance more than street driving.
I agree with the sentiment above that it would be a good idea to drop back to a set of "normal" SU's and see what happens. Just so many variables...