1. Most manufacturers will list the proper weight distribution for their chassis’. 40/60 to 43/57 is common. Thats a good starting point, then let the handling and stopwatch be the guide.
2. Go ahead and buy 4 bathroom scales. You really need to have all four wheels scaled simultainiously. Bathroom scales are a good starter set-up, but know they will not be 100% accurate. Calibration from scale to scale, and accuracy as weight is added tend to be “fuzzy”. With that in mind – go cheap with a bathroom scale. I’m talking $10-15 apiece cheap. If you’re spending more, go with a shipping scale (@ $50-ish apeice). Next step would be used racing scales at $400-700 a set. Finally new racing scales at $700-1500 a set.
So for a karter new to scales, a bathroom scale set will intro you to scaling, get you in the ballpark, and show any gross weight issues. Also get a nice 4′ level and a dozen 1’x1′ floor tiles to level the scales on your floor.
Don’t even begin to think the bathroom scale set-up is scientific. Its not. Thats why the racing scales cost so much – accuracy. Just assume each scale is accurate to within +/- 3lbs, and your total class weight is +/- 15lbs. In other words don’t think your total is making you class legal! Also, to check for consistancy, after you weight the kart, rotate the scales so each is under a different corner of the kart and double check the weights. Doing this a few times will reveal if you have a scale way off from the rest.