You need to get your friends to put it back to as close as possible to where it was before they started. From there, start with the basics by checking the plug gaps, checking the timing at idle and at around 2000 RPMs. Then make only "one" change at a time a see what happens. If the first change doesn't make a difference, put it back where it was and try something different. The mistake some people make is doing wholesale changes and screwing everything up. It took me a while when I first started to adopt the mentality of "one change" at a time.