Go to the store and buy a turkey baster, remove the rubber squeeze ball on top and throw it away
Remove the top screw at rear master cylinder/pump, turn and screw in tip of turkey baster
Fill it up like a funnel, all the way to the top
Remove the top screws Walt said at the rear calipers, you can only bleed the top ones
Pick up the kart from the front and put a 4×4 under the frame to create higher level
Let the fluid run at the caliper top bolts and pay close attention to the turkey baster, not to run dry. I would run 2 cycles of the funnel to clean all that junk out, and to make sure no more air is in the system.
Put the screw back in at the top part whichever rear caliper you decided to bleed first
Repeat the same procedure at the other side caliper.
Seal the other side caliper bleed screw when done, please remember never to run the turkey baster funnel dry, in fact when you’re done, please make sure there’s a bit left inside of it, so that when you remove funnel it will drain out of it, rather than not having enough fluid and letting air into the master cylinder.
When turkey baster/funnel removed, please re install filler screw back to master cylinder, make sure no debris goes inside, and pay attention so that washer or seal is still in good shape
Rear brake system completed, Congratulations, now move on to front brake system:
Remove piece of 2×4 from front of kart
Remove front master cylinder filler screw, install that FAMOUS TURKEY BASTER
Remove 2 front caliper top allen head bolts, fill up turkey baster with brake fluid
This may be a bit harder to bleed, since level is about the same for gravity bleed
Blow with your mouth on top of that famous turkey baster to force fluid flow
Sometimes you gotta do that to get’em going
Same procedure, just do 2 cycles and seal it back up, and be done with it.
That’s my 2 cents, good luck!
If that doesn’t work, then by the look of your calipers on the outside, then you may have to take all the calipers apart, hone them and rebuild the seals, and master cylinder too
And when you’re done, go back to your new best friend