Re: Standard upgrades?
These guys are right on the money for standard performance mods. as far as some small technical stuff that I would personally recommend to solve a problem before you have it;
-replace the ragjoint sprocket assembly with a manic or similar hub adapter. the ragjoint can ruin your wheel in my experience. others have had good luck though. an HD wheel will hold up just fine.
-grease all your cables (throttle, clutch, even brakes) they can fray inside the housing over time if you dont and the last thing you want is any one of those cables breaking mid ride.
-install an inline fuel filter and replace stock petcock. the stock pet is pathetic, and the filter inside it is a joke. the filter can clog and the petcock can leak.
-people swear by loctite, ive never used it. just make sure your bolts are tight every other ride or so.
theres a million and one other things to do to these engines, it all depends on what you want out of it. ive built little put puts for friends that ran about $300 when all was said and done, and ive built two bikes that would have ran over $2000 if i bought everything off the shelf. which leads me to my biggest tip;
as far as bike parts go, thrift shops and ebay/craigslist are your friends
as for engine parts, if you cant find it cheap on ebay or craigs search different vendor sites. theyre all competitive and the prices change so you can usually find one thats got a good deal on whatever your looking for.
Good luck and happy riding!