Porting 

Porting is very convenient for the CR500 because you don't need to resleeve the cylinder. The cylinder doesn't have a layer of nikasil like the kx500. It's also cheaper to port a CR500 than a kx500 because of that reason. There are definetly many businesses out there that offer porting services. Some businesses will offer extreme port jobs that make a CR500 a CR640!!! Yes you heard right porting an engine up to 640 ccs. Depending on how you port the CR 500 you could get 90hp out of it.  

 

Gearing  

Stock speed is about 80-85 mph. But thats only with 14/49 gearing. 100+ mph speeds are pretty easy to get just by changing the gearing. Just by ordering a smaller rear sprocket and a bigger front sprocket you can dramatically change your speed.

 

Carburation 

 You can get a little more HP out of it by getting a bigger carb like the Keihen PWK 39.5 or 40mm carb. Or mikuni carbs work well.

 

Decompression valve

If you ever tried kick starting a CR500 you would know how useful a decompression valve would be. Starting one with a decompression valve makes a night and day difference. Some businesses offer to fabricate a decompression valve on your head for decent prices.

 

Oversized radiators   

Getting oversized radiators will definetly benefit the engine to stay cool better therefore perform better.  For the long run, the investment is worth it.