Hello, what would people say is the most effective way to make a dt100 slightly more pleasant to ride at higher rpms.  I have a home made seat which to be fair isn’t that good and  is probably not absorbing much. I am fairly sure I changed the front sprocket to lower the revs but that was a while ago. Or is that how it is at 30 mph plus? 
many thanks Tunnie

If it's engine vibration then my first place to look is loose engine mount bolts. Bottom back one could easily be missed. Other than 'that', loose left side crank bearing comes to mind & can easily check by grabbing the magneto flywheel & try for up & down movement. I've got a 100 LS3 Yamy with a worn left side bearing & vibes but mainly at just above idle, but that has a lot of movement because the crank starts turning inside the bearing so wears the shaft not realy the bearing. Caused by bad machining tolerances from the factory. Had that lot with smaller 50cc scooters too in the early days. Anyway--hope yours is only caused by seat too thin on padding.

If crank is true and bolts are tight the smaller engines tend to be sewing machine smooth...

You mention 30 mph and not "rpm" which makes me wonder if maybe a tire or something is way out of balance?

Thanks for info most appreciated 
Tunnie