It definitely happens a lot on my kart. I think I've gotten to the point where most major issues are fixed, but I fixed and replaced a lot (both out of necessity and for modification's sake). Off the top of my head...
- Replaced engine (Robin Subaru 169cc to Predator 212cc Stage 1)
- Replaced bent axle with rusted-on rim hub after rear tire flew off at 30 mph
- Replaced all 4 rims
- Replaced all 4 knobby tires with slicks
- Replaced bent brake rotor and brake caliper
- Reconnected brake linkage that wiggled loose while riding (lost all brakes heading into a sharp corner at 35-ish mph)
- Spent about a month trying to figure out why my chain kept popping off (CVT bracket kept tagging it causing it to pop off, just removed bracket)
- Replaced chain that snapped and locked up rear tires sending me into a tree
- Welded rear bar after bracket holding it on snapped off
- Replaced carburetor after kart refused to start after sitting for a few months (small carbs don't like sitting too long...apparently...)
And that's just what I can remember. Point is, it may be frustrating but not only did I learn a lot about fixing stuff in the time I've owned this kart, but I've also gotten a sense of satisfaction in taking a run down go-kart that could barely move under it's own power when I bought it and turning it into a 40 mph mini-buggy that loves to slide around corners. Trust me, keep fixing - you already have a nice kart on your hands. As you said, reliability will increase as you replace parts. Soon you will have very few issues and a lot more fun.