Agreed. Lots of possible causes. Favorite one is air leak at head/exhaust.
Can also be air leak head/carb, incorrect ignition etc.
I seem to remember being told to spray something in the area of the suspected leak - was it WD or Redex? And listen for a change in the engine note - ah yes that would only be for head/carb presumably, as the exhaust would be gases leaking
out.....
Oh and I once had a problem which took me ages to diagnose and turned out to be a loose sparkplug!
Oh and then there's loose fuse, loose earth lead, battery lead..... or dry joint in any of those