After the winter this engine wouldn't idle, so I rebuilt the carburetor with an aftermarket kit. (Mercarb not Rochester) Now it starts right away and idles smoothly. But when running, it will stall with increased throttle. We can be going great at 50% throttle, and when I increase to 60% it just dies. I thought maybe the throttle cable was stiff and causing the ignition kill switch to kill the engine, but that seems fine. Now I'm wondering if the accelerator pump is not working properly. When taking off, from idle to 20% throttle it doesn't stall, but going from 50% to 60% or from 60% to 70% it stalls. If we very gradually open the throttle it is fine. Somewhere I read that the aftermarket accelerator pumps aren't as good as stock. Or is there something else that it could be?