Extrusion Problems

Everything is with a prusa i3 and Marlin Firmware

Just wondering what speed I should be running a bowden extruder at. Could i please have the answer with the coding lines and numbers please. If it would help I can post the relevant (what i hope is relevant) sections of my current code.

The hardware issue is just my extrusion is jamming the nozzle and is just creating a big blockage. This I hope can be solved with a firmware fix.

I'm willing to try almost anything at this stage to get it up and running.

Thanks