I'm assuming you've checked out all the BullGear internal replacement parts but either can't or don't want to go down that route at the moment?
What are the internals on this one anyway, is it the "loading platform" type? In which case, could you substitute it with the MAG brand version (I think you'd need to retain the section where it meets the actual gun). It's a bit more straightforward.
If you don't want to look at buying anything, just mods, then I'd probably be looking at making sure the bowden feed spring is good (can cause feed issues if it's been stretched) and looking at wiring options. Is it sound activated, pressure switch, direct wired? Other possibilities are jamming due to dirt/off sized BB's. Usually you can pull the spring from the gun portion and determine if it's a jam in that tube or internally, which might at least give you some pointers.