Hi I have had rear caliper kit fitted by trials shop I've tried bleeding brake several times keep getting same result poor brake today took off caliper removed pads pistons only move slightly even with no resistance they don't come right out should I be looking at master cylinder or is there still air system I have used large syringe backwards and from reservoir no air bubbles all looks good any help would be appreciated cheers mark 

 What year Beta? Fitted with new pads?

2006 rev 3 

Yes new pads sorry first time posting new to this 

 The Rev 3`s can be hard. You might actually save time by removing the whole system off the bike hanging it by the caliper bleeding and reinstall. If not, lift the rear of the bike so the caliper is higher than the m/c. Also remove the brake rod and use a philips screwdriver to pump it. Burb the m/c by loosening the brake hose and re-tighten.  It`s best to use a 3 foot clear hose and wrap it up and over the rear fender. Gravity will then work in your favor. It takes time, just be patient.

Cheers mate think Ill try screwdriver next one last thing why won't pistons come out even with pads out is that just air 

 Oh, I am sure. They can be real stubborn. Is that still the 4 pot?

Sorry mate not sure what 4 pot is  there are 2 pistons on each caliper the pistons only move a few mm  in and out not enough to lock wheel they don't keep coming out  I'll have ago after work tomorrow  cant take it anywhere due to lockdown thanks for advice ??

4 pistons vs 2 pistons. Could not remember when they went back to the 2 piston design. Good luck.

Hi

Just bleed  mine it takes time and you need to be patient. 

Good luck 

I take it off and hang it ,back bleed it and move the master cylinder around and let the air make its way to the master cylinder, keep back bleeding

If you've got some pressure but the pistons just move out and then back and don't easily pop out then it's likely that the grooves for the seals need cleaning. I did mine and even though they looked clean to the eye, the amount of crap I could scrape and wipe out was unbelievable. This can make the seals fit a bit too tightly on the pistons and not let them slide out properly. Unless the dealer/shop was really good, they probably just chucked the new seals and pistons in. 

A good indicator of this is when you pump then with no cap on the master cylinder and no pads fitted and the pistons move out then on release of the pedal, they immediately go back in to the same spot. It's the friction and the elasticity of the seals that pulls them back. 

The only other thing is if the hole in the master cylinder piston (or anywhere in the line) is blocked, stopping fluid from being sucked down. But if you can easily back bleed it, that shouldn't be the problem.