Did your friends car start doing the same carzy stuff after taking jumps?

I dont know this engine or car but from the sound of what you are saying something got loose. Most probably the carb.
Also, did you try with a new glow plug.
I know it may sound stupid (and probably have already don so) but is your glow plug heater charged.
Last thing that passes though my ind is the fuel. How long do you have it and did by any chance leave it on storage no closed tight enough.