hydraulic clutch problems

I'm the owner of a AMW Spirit custom 5 speed motorcycle with a S&S
1400 cc engine. Recently the following problem occurs:
When the engine is warm (approx after 60 min of riding) the clutch
handling becomes quite heavy. Even shifting into gears becomes very
tiresome.
However, when the motor is cold the gear shifting and clutch handling
is all the different, even easy. I've checked all fluid levels and
also attempted to bleed the hydraulic systems, with no positive
results. I've even checked the oil pump to see that it's working
correctly.
Could I receive any advise or suggestions how to deal with this
problem?

 

You do have a hydraulic clutch on there, right? I've seen hydraulic
clutches in cars get soft when they get hot, but that's right before
one of the cylinders fails altogether.

That said, I doubt that this is your problem at all. Rather, I'd
check the primary belt or chain adjustment. These will get a bit
tighter when the machine warms up, due to expansion of the primary
case. Check the tension as recommended by the builder or primary
drive manufacturer. Normally these won't get tighter with use, but
you could have worn something out in there, or you could have tight
links if you have a chain.

 

The bike is belt driven.
Thanks for the suggestion, I'll start on it first thing this weekend