Casterton motorcycles

Check your clutch adjustment, being an older bike could be fairly worn in there 

Check your filter in the fuel pump unit, sounds like it’s full of crap 

What you need to do is check your voltage to the shift motor when trying to down shift, if you have voltage will need to check brushes inside of shift motor And also check the grease on the gears. If there is no voltage will need to check resistance to angle sensor and sensor itself.