The tubes will increase spine. I'm a lefty too. Your weighted arrows are stiff. You'll have to add point weight to compensate or go down an arrow spine and try again. I tried them for a spell and they just gave me fits and only worked decent if I used them with higher draw weight bows where I was trying to achieve a very heavy, high point weight arrow, that was when I was playing with high draw weight big game setups as a fun experiment. I abandoned the tubes. I really don't think they are worth messing with unless you're trying to build 6 or 700+ grain arrows for 60,70 or more pound bows.
If you're shooting 40# 490 ought to be "enough". You just need to redesign how you get there. If all the weight is in the shaft and not enough in the tip you'll get crappy flight and penetration.