New brake pads binding

[Hustler]

I assume this is the correct place to post this type of question.
Yamaha TTR250 2001, fitted new rear brake pads today and went for a spin to test them and found they were binding badly.
I was riding along and it was as if the brake was slightly on, but they did work when I applied them. The rear disc was also incredibly hot.
So back home and found another new set of pads that appeared slightly thinner so swapped them over but had exactly the same problem.
Disc appears straight and true although I haven't taken it off and placed in on a flat surface to check.
I did syphon off a little brake fluid to ensure it wasn't overfull as the new pads would be thicker than the original replaced set.
Have only had the bike a week so whilst I assume the old set worked normally I have no experience of actually using them. I have still got the old set although they are very worn but haven't tried putting them back to see what happens.
Distance travelled for each "test" say 6 miles ish.
Any hints, tips, ideas, magic potions most welcome, thank you.

 

[bumpmuncher]

on all the yams i have had its usually down to the pistons binding. removing the pistons and polishing the crap off puting them back together then bleed usually did the trick. Bm

 

[Hustler]

on all the yams i have had its usually down to the pistons binding. removing the pistons and polishing the crap off puting them back together then bleed usually did the trick. Bm

Thanks bump, yes, thinking about it that does make sense.
I pushed the bike around in the workshop this morning and it was very hard to move as the brake seems to be solidly on now.
A bit more spanner twirling coming up then.