Yes, they would have an effect on the bottom end response. Jetting your carbs pertains to throttle postion, not RPM's. The main jet does in fact start coming into play at 1/4 throttle, may even be a little less, and the needle is what controls how much gas is coming out of the main. The needle doesn't completely plug up the main jet when the throttle is "closed", gas will still flow past it if air is pulling it out. As soon as you hit the throttle, it starts lifting the needle up which sits in the main jet, so yes, zonker is right, the main and needle do have a role in bottom end performance...chill out man :thumbsup: