Probably for peace of mind use silicone fluid dot 5.0
Tonykart/OTK have messed around with brake fluid spec. over the years starting? with glycol based fluid dot3.dot 4. then going to silicon dot 5.0 and currently dot 5.1 which I class as glycol. The spec in 2014 was apparently Dot 5.0 silicone.
As I understand it, if any brake fluid is going to attack any seals it is the glycol fluids. Dot 5.0 silicon is safe with everything.
However, personally, I doubt if there has been a European kart brake made in the last 20 years with seals that would be attacked by Dot3,Dot4,Dot 5.0 or Dot 5.1 fluid. but…
So, you have a BSM4 master cylinder (Pumper type with reservoir) and a BS6 caliper (Self adjusting, no pad pull off springs ?
Good pics. of all the brakes at www.cometkartsales.com /Tonykart parts.
That system SHOULD bleed normally. Fill up reservoir. Open 1bleed nipple at caliper. Actuate the master cylinder with long steady strokes until fluid comes out of the nipple free of air. Keep reservoir topped up. Close bleed nipple. Repeat for other side of caliper. Done.
But if you’ve done all that and got nowhere.
Disconnect operating cable/ rod at m/cyl and check that m/ cyl piston is returning fully and freely.
Close caliper bleed nipple at end of each stroke and open at beginning of next stroke.
Use a rubber bleeder pipe on the nipple. the type with a plugged end and a slit in the side which acts as a non return valve.
Still no joy.
Disconnect caliper line at m/ cyl and operate m/cyl with your finger over the outlet. Down stroke will blow air/ fluid past your finger, return stroke will pull fluid from reservoir into the bore. Once pumping well reconnect caliper line. Sometimes m/cyl needs ‘priming’
Bleeding brakes is usually a struggle!