Bo we're actually technical support. The 725 Road Demon series carburetors are designed for larger cubic inch milder engines. We're dealing with multiple problems here, a smaller cubic inch engine, with a more radical camshaft, and an airgap intake manifold which acts like an open plenum intake. The decrease in air velocity, and only running 11 degrees of initial timing are causing the rich idle, and lean off idle conditions you're seeing. Increasing the ignition timing a few degrees to about 14 should help some, but you'd need to increase the squirter size if the only time your backfire is happening is when you step on the throttle quickly. We build our carburetors more specifically then other manufactures, this gives us a smaller window where they will work properly. You may be able to crutch the combination to get it to work better with this carburetor, but it will not work as well as it would with a different carburetor. On this combination we would have recommended a 650 Speed Demon carburetor.