hi everyone. This is my first time on this forum so I appoligise if I do this incorrectly.

i have a really neat Yamaha XT250H 1981, it starts easy, idles great, plenty of compression, standard carb and jets,  gears (16 front 47 rear) 

My problem is that the bike is gutless and 60klms is top speed.

Any tips??  

Check the gearing, I thought an Enduro would have lower than 16-47.

Also try checking for air leaks on carb boots and the air box, that can be done by spraying starter fluid (VERY CAREFULLY) around these areas whilst the bike is running, you'll know it's leaking if the engine speed changes. Also check valve lash, they may be too tight causeing the valves not to close properly. But I kinda doubt it's an air leaks since you said it idles well and starts easy.

Have you checked the spark timing? Since it's from 81 it'll have CDI, I've had friends who've had issues with bad units, or even just having the bullet connectiors plugged in wrong.

Apart from that I'm not sure.

its very old...perhaps the bore or rings are worn, perhaps a compression check might be a way forward too?