I'm far from an expert, but it seems that these are budget bikes without many easy upgrades that significantly increase power. For most parts, the question "What _____ should I upgrade to?
" is answered with "There isn't really anything that performs better than stock.
" Based on what people like FOG say, there simply isn't that much headroom left in the engine for increasing performance; it's not that the ____ is too small, it's that the engine is pretty much maxed out already, so a bigger ____ doesn't really help anything.
Every factory vehicle has compromises to meet budget and legal requirements. I'm sure there are many parts that can be improved over stock. The FOG airbox mod is one basic example. However, it comes down to how much improvement you get vs. how much you spend on the improvement. I just found this carb upgrade
for $500-$600 (depending on specifics). I honestly don't know enough about carbs to know if that would be an overall improvement (for street or track). However, that's a pretty good chunk of money (10% of the cost of a brand new bike, more than some people paid for their used bikes). Are you really going to get a 10% improvement over stock with that? Maybe if you spend a few hundred more on an exhaust and jet kit, it might help more. Now you're up to $1,000+ spent and how much better is the bike?
I'm not saying that everything's been done and there's no way to improve anything. However, it seems like the relatively cheap, easy basics have all been tried over the past 25 years and don't significantly improve things. When you factor in the price and role of the average EX500, it's just not worth it to spend so much money for such small improvements. It might be different if it's an old trashed bike where everything needs to be replaced anyway or you're racing professionally and looking for every last tweak to wring an extra drop of power out of it.
Personally, I think my biggest dream is fuel injection. In my eyes, carbs are cheap and "good enough", nothing more. Once you understand FI tuning, it's so nice to work with. With a computer controlling it, you can adjust the fueling for a multitude of engine loads and speeds. Whereas there are a couple ways to adjust how much fuel a carb injects, FI allows for nearly infinite adjustment. The biggest issue with putting FI on an EX500 is probably retrofitting all the electronics and sensors needed to give the computer good information to base its fueling on. Again, with all the time and money it would take to set things up right, sticking with the cheap carbs seems like a better value, even though I know FI would be much better.