Art:
If you in fact actually have racing clutch, some of them do not have the coil springs in the hub or the wafer spring (marcel) between the two friction surfaces. The lack of these means that is as you have discovered "ON or OFF". They do not allow for slippage without excessive heat buildup. The trade off is generally greater torque capacity in a lighter package, with less rotatioanal weight.
Rick
PS: Just another point to keep in mind: Sometimes the disc or the flywheel will become glazed due to contamination (
oil) or heat from slippage (intentional or not) in spots and will cause poor engagement or chatter while engaging.